Method and device for extracting an analyte

ABSTRACT

The invention provides extraction columns for the purification of an analyte (e.g., a biological macromolecule, such as a peptide, protein or nucleic acid) from a sample solution, as well as methods for making and using such columns. The columns typically include a bed of extraction media positioned in the column between two frits. In some embodiments, the extraction columns employ modified pipette tips as column bodies. In some embodiments, the invention provides methods characterized by the elution of analyte in a small volume of liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit of U.S. patentapplication Ser. No. 10/896,382, filed Jul. 20, 2004; U.S. patentapplication Ser. No. 10/620,155, filed Jul. 14, 2003; and U.S.Provisional Patent Application Ser. No. 60/570,302, filed May 12, 2004,the disclosures of which are incorporated herein by reference in theirentirety for all purposes.

FIELD OF THE INVENTION

This invention relates to methods and devices for extracting an analytefrom a sample solution. The analytes can include biomolecules,particularly biological macromolecules such as proteins and peptides.The device and method of this invention are particularly useful inproteomics for sample preparation and analysis with analyticaltechnologies employing biochips, mass spectrometry and otherinstrumentation.

BACKGROUND OF THE INVENTION

Solid phase extraction is a powerful technology for purifying andconcentrating analytes, including biomolecules. For example, it is oneof the primary tools used for preparing protein samples prior toanalysis by any of a variety of analytical techniques, including massspectrometry, surface plasmon resonance, nuclear magnetic resonance,x-ray crystallography, and the like. With these techniques, typicallyonly a small volume of sample is required. However, it is often criticalthat interfering contaminants be removed from the sample and that theanalyte of interest is present at some minimum concentration. Thus,sample preparation methods are needed the permit the purification andconcentration of small volume samples with minimal sample loss.

The subject invention involves methods and devices for extracting ananalyte from a sample solution using a packed bed of extraction media,e.g., a bed of gel-type beads derivatized with a group having anaffinity for an analyte of interest. These methods, and the relateddevices and reagents, will be of particular interest to the lifescientist, since they provide a powerful technology for purifying,concentrating and analyzing biomolecules and other analytes of interest.However, the methods, devices and reagents are not limited to use in thebiological sciences, and can find wide application in a variety ofpreparative and analytical contexts.

SUMMARY OF THE INVENTION

The invention provides separation columns, many of which arecharacterized by the use of relatively small beds of extraction media.

In one embodiment, the instant invention provides an extraction columncomprising: a column body having an open upper end, an open lower end,and an open channel between the upper and lower end of the column body;a bottom frit bonded to and extending across the open channel; a topfrit bonded to and extending across the open channel between the bottomfrit and the open upper end of the column body, the top frit having alow pore volume, wherein the top frit, bottom frit, and column bodydefine an extraction media chamber; and a bed of extraction mediapositioned inside the extraction media chamber, said bed of extractionmedia having a volume of less than about 100 μL.

In some embodiments, the bed of extraction media comprises a packed bedof resin beads. Non-limiting examples of resin beads include gel resins,pellicular resins and macroporous resins.

In certain preferred embodiments of the invention, the column comprisesa packed bed of gel resin beads, e.g., agarose- or sepharose-basedresins.

In certain embodiments of the invention, the bed of extraction media hasa volume of between about 0.1 μL and 100 μL, between about 0.1 μL and 20μL, between about 0.1 μL and 10 μL, between about 1 μL and 100 μL,between about 1 μL and 20 μL, between about 1 μL and 10 μL, or betweenabout 3 μL and 10 μL.

In certain embodiments of the invention, the bottom frit and/or the topfrit has/have a low pore volume.

In certain embodiments of the invention, the bottom frit and/or the topfrit is/are less than 200 microns thick.

In certain embodiments of the invention, the bottom frit and/or the topfrit has/have a pore volume equal to 10% or less of the interstitialvolume of the bed of extraction media.

In certain embodiments of the invention, the bottom frit and/or the topfrit has/have a pore volume of 0.5 microliters or less.

In certain embodiments of the invention, the bottom frit and/or the topfrit is/are a membrane screen, e.g., a nylon or polyester wovenmembrane.

In certain embodiments of the invention, the extraction media comprisesan affinity binding group having an affinity for a biological moleculeof interest, e.g., Protein A, Protein G and an immobilized metal.

In certain embodiments of the invention, the column body comprises apolycarbonate, polypropylene or polyethylene material.

In certain embodiments of the invention, the column body comprises aluer adapter, a syringe or a pipette tip.

In certain embodiments of the invention, the upper end of the columnbody is attached to a pump for aspirating fluid through the lower end ofthe column body, e.g., a pipettor, a syringe, a peristaltic pump, anelectrokinetic pump, or an induction based fluidics pump.

In certain embodiments of the invention, the column comprises a lowertubular member comprising: the lower end of the column body, a firstengaging end, and a lower open channel between the lower end of thecolumn body and the first engaging end; and an upper tubular membercomprising the upper end of the column body, a second engaging end, andan upper open channel between the upper end of the column body and thesecond engaging end, the top membrane screen of the extraction columnbonded to and extending across the upper open channel at the secondengaging end; wherein the first engaging end engages the second engagingend to form a sealing engagement. In some of these embodiments, thefirst engaging end has an inner diameter that matches the externaldiameter of the second engaging end, and wherein the first engaging endreceives the second engaging end in a telescoping relation. The firstengaging end optionally has a tapered bore that matches a taperedexternal surface of the second engaging end.

The invention further provides a method for extracting an analyte from asample solution comprising the steps of introducing a sample solutioncontaining an analyte into the packed bed of extraction media of anextraction column of the invention, wherein the extraction mediacomprises an affinity binding group having an affinity for the analyte,whereby at least some fraction of the analyte is adsorbed to theextraction media; substantially evacuating the sample solution from thebed of extraction media, leaving the adsorbed analyte bound to theextraction media; introducing a desorption solvent into the bed ofextraction media, whereby at least some fraction of the bound analyte isdesorbed from the extraction media into the desorption solvent; andeluting the desorption solvent containing the desorbed analyte from thebed of extraction media.

In certain embodiments of the method, the extraction column is attachedto a pump at one end and one or more of the solvents, e.g., thedesorption solvent and/or the sample solution, is aspirated anddischarged through the lower end of the column.

In certain embodiments of the method, the extaction media is washedbetween the sample loading and desorption steps.

In certain embodiments of the method, the volume of desorption solventintroduced into the column is less than 3-fold greater the interstitialvolume of the packed bed of extraction media.

In certain embodiments of the method, the volume of desorption solventintroduced into the column is less than the interstitial volume of thepacked bed of extraction media.

In certain embodiments of the method, the desorption solvent isaspirated and discharged from the column more than once, i.e., aplurality of in/out cycles are employed to pass the solvent back andforth through the bed more than once.

In certain embodiments of the method, the analyte is a biologicalmacromolecule, e.g, a protein.

In certain embodiments of the method, the volume of desorption solventintroduced into the column is between 10 and 200% of the interstitialvolume of the packed bed of extraction media, or between 20 and 100% ofthe interstitial volume of the packed bed of extraction media, orbetween 10 and 50% of the interstitial volume of the packed bed ofextraction media.

In certain embodiments of the method, volume of desorption solventintroduced into the column is less than 20 μL, e.g, between 1 μL and 15μL, between 0.1 μL and 10 μL, or between 0.1 μL and 2 μL.

In certain embodiments of the method, the enrichment factor of themethod is at least 10, at least 100, at least 1000, or at least 10,000.

In certain embodiments of the method, the desorption solution is passedthrough the bed of extraction media at a linear velocity of greater than10 cm/min.

In certain embodiments of the method, prior to the desorption step a gasis passed through the bed of extraction media, resulting in theevacuation of a majority of bulk liquid residing in said interstitialvolume. The bulk liquid can comprise sample solution and/or washsolution. The gas can comprise nitrogen.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an embodiment of the invention where the extractioncolumn body is constructed from a tapered pipette tip.

FIG. 2 is an enlarged view of the extraction column of FIG. 1.

FIG. 3 depicts an embodiment of the invention where the extractioncolumn is constructed from two cylindrical members.

FIG. 4 depicts a syringe pump embodiment of the invention with acylindrical bed of solid phase media in the tip.

FIG. 5. is an enlarged view of the extraction column element of thesyringe pump embodiment of FIG. 4.

FIGS. 6-10 show successive stages in the construction of the embodimentdepicted in FIGS. 1 and 2.

FIG. 11 depicts an embodiment of the invention with a straightconnection configuration as described in Example 8.

FIG. 12 depicts an embodiment of the invention with an end cap andretainer ring configuration as described in Example 9.

FIG. 13 depicts an example of a multiplexed extraction apparatus.

FIG. 14 is an SDS-PAGE gel referred to in Example 11.

FIG. 15 depicts a pipette tip column attached to a pipettor, and pointsout the head space.

FIG. 16 plots the head pressure of a pipette tip column, the chambervolume of a syringe attached to the pipette tip column, and the volumeof liquid in the column, all as a function of time, during a typicalextraction process.

FIG. 17 depicts an embodiment of the invention where the extractioncolumn can take the form of a pipette tip.

FIG. 18 depicts a preferred embodiment of the general embodimentdepicted in FIG. 17.

FIG. 19 depicts a pipette tip column attached to an apparatus fordetermining column back pressure.

FIGS. 20 and 21 depict a method for determining the back pressure of amembrane frit as described in Example 12.

FIG. 22 depicts a porous frit, the back pressure of which is to bedetermined as described in Example 12.

FIG. 23 depicts a pipette tip column to be stored in a wet state.

FIGS. 24 through 27 depict a method for positioning pipette tip columnsin a multiplexed extraction process.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

This invention relates to methods and devices for extracting an analytefrom a sample solution. The analytes can include biomolecules,particularly biological macromolecules such as proteins and peptides,polynucleotides, lipids and polysaccharides. The device and method ofthis invention are particularly useful in proteomics for samplepreparation and analysis with analytical technologies employingbiochips, mass spectrometry and other instrumentation. The extractionprocess generally results in the enrichment, concentration, and/orpurification of an analyte or analytes of interest.

In U.S. patent application Ser. No. 10/620,155, incorporated byreference herein in its entirety, methods and devices for performing lowdead column extractions are described. The instant specification, interalia, expands upon the concepts described in that application.

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to specific embodimentsdescribed herein. It is also to be understood that the terminology usedherein for the purpose of describing particular embodiments is notintended to be limiting. As used in this specification and the appendedclaims, the singular forms “a”, “an” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to polymer bearing a protected carbonyl would include apolymer bearing two or more protected carbonyls, and the like.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention pertains. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, specific examples ofappropriate materials and methods are described herein.

Definitions

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set outbelow.

The term “bed volume” as used herein is defined as the volume of a bedof extraction media in an extraction column. Depending on how denselythe bed is packed, the volume of the extraction media in the column bedis typically about one third to two thirds of the total bed volume; wellpacked beds have less space between the beads and hence generally havelower interstital volumes.

The term “interstitial volume” of the bed refers to the volume of thebed of extraction media that is accessible to solvent, e.g, aqueoussample solutions, wash solutions and desorption solvents. For example,in the case where the extraction media is a chromatography bead (e.g.,agarose or sepharose), the interstitial volume of the bed constitutesthe solvent accessible volume between the beads, as well as any solventaccessible internal regions of the bead, e.g, solvent accessible pores.The interstitial volume of the bed represents the minimum volume ofliquid required to saturate the column bed.

The term “dead volume” as used herein with respect to a column isdefined as the interstitial volume of the extraction bed, tubes,membrane or fits, and passageways in a column. Some preferredembodiments of the invention involve the use of low dead volume columns,as described in more detail in U.S. patent application Ser. No.10/620,155.

The term “elution volume” as used herein is defined as the volume ofdesorption or elution liquid into which the analytes are desorbed andcollected. The terms “desorption solvent,” “elution liquid” and the likeare used interchangeably herein.

The term “enrichment factor” as used herein is defined as the ratio ofthe sample volume divided by the elution volume, assuming that there isno contribution of liquid coming from the dead volume. To the extentthat the dead volume either dilutes the analytes or prevents completeadsorption, the enrichment factor is reduced.

The terms “extraction column” and “extraction tip” as used herein aredefined as a column device used in combination with a pump, the columndevice containing a bed of solid phase extraction material, i.e.,extraction media.

The term “frit” as used herein are defined as porous material forholding the extraction media in place in a column. An extraction mediachamber is typically defined by a top and bottom frit positioned in anextraction column. In preferred embodiments of the invention the frit isa thin, low pore volume filter, e.g, a membrane screen.

The term “lower column body” as used herein is defined as the column bedand bottom membrane screen of a column.

The term “membrane screen” as used herein is defined as a woven ornon-woven fabric or screen for holding the column packing in place inthe column bed, the membranes having a low dead volume. The membranesare of sufficient strength to withstand packing and use of the columnbed and of sufficient porosity to allow passage of liquids through thecolumn bed. The membrane is thin enough so that it can be sealed aroundthe perimeter or circumference of the membrane screen so that theliquids flow through the screen.

The term “sample volume”, as used herein is defined as the volume of theliquid of the original sample solution from which the analytes areseparated or purified.

The term “upper column body”, as used herein is defined as the chamberand top membrane screen of a column.

The term “biomolecule” as used herein refers to biomolecule derived froma biological system. The term includes biological macromolecules, suchas a proteins, peptides, and nucleic acids.

The term “protein chip” is defined as a small plate or surface uponwhich an array of separated, discrete protein samples are to bedeposited or have been deposited. These protein samples are typicallysmall and are sometimes referred to as “dots.” In general, a chipbearing an array of discrete proteins is designed to be contacted with asample having one or more biomolecules which may or may not have thecapability of binding to the surface of one or more of the dots, and theoccurrence or absence of such binding on each dot is subsequentlydetermined. A reference that describes the general types and functionsof protein chips is Gavin MacBeath, Nature Genetics Supplement, 32:526(2002).

Extraction Columns

In accordance with the present invention there may be employedconventional chemistry, biological and analytical techniques within theskill of the art. Such techniques are explained fully in the literature.See, e.g. Chromatography, 5^(th) edition, PART A: FUNDAMENTALS ANDTECHNIQUES, editor: E. Heftmann, Elsevier Science Publishing Company,New York (1992); ADVANCED CHROMATOGRAPHIC AND ELECTROMIGRATION METHODSIN BIOSCIENCES, editor: Z. Deyl, Elsevier Science BV, Amsterdam, TheNetherlands, (1998); CHROMATOGRAPHY TODAY, Colin F. Poole and Salwa K.Poole, and Elsevier Science Publishing Company, New York, (1991).

In some embodiments of the subject invention the packed bed ofextraction media is contained in a column, e.g., a low dead volumecolumn. Non-limiting examples of suitable columns, particularly low deadvolume columns, are presented herein. It is to be understood that thesubject invention is not to be construed as limited to the use ofextraction beds in low dead volume columns, or in columns in general.For example, the invention is equally applicable to use with a packedbed of extraction media as a component of a multi-well plate.

Column Body

The column body is a tube having two open ends connected by an openchannel, sometimes referred to as a through passageway. The tube can bein any shape, including but not limited to cylindrical orfrustroconical, and of any dimensions consistent with the function ofthe column as described herein. In some preferred embodiments of theinvention the column body takes the form of a pipette tip, a syringe, aluer adapter or similar tubular bodies. In embodiments where the columnbody is a pipette tip, the end of the tip wherein the bed of extractionmedia is placed can take any of a number of geometries, e.g., it can betapered or cylindrical. In some case a cylindrical channel of relativelyconstant radius can be preferable to a tapered tip, for a variety ofreason, e.g., solution flows through the bed at a uniform rate, ratherthan varying as a function of a variable channel diameter.

In some embodiments, one of the open ends of the column, sometimesreferred to herein as the open upper end of the column, is adapted forattachment to a pump, either directly or indirectly. In some embodimentsof the invention the upper open end is operatively attached to a pump,whereby the pump can be used for aspirating (i.e., drawing) a fluid intothe extraction column through the open lower end of the column, andoptionally for discharging (i.e., expelling) fluid out through the openlower end of the column. Thus, it is a feature certain embodiments ofthe present invention that fluid enters and exits the extraction columnthrough the same open end of the column, typically the open lower end.This is in contradistinction with the operation of some extractioncolumns, where fluid enters the column through one open end and exitsthrough the other end after traveling through an extraction media, i.e.,similar to conventional column chromatography. The fluid can be aliquid, such as a sample solution, wash solution or desorption solvent.

In other embodiments of the present invention, fluid enters the columnthrough one end and exits through the other. In some embodiments, theinvention provides extraction methods that involve a hybrid approach;that is, one or more fluids enter the column through one end and exitthrough the other, and one more fluids enter and exit the column throughthe same open end of the column, e.g., the lower end. Thus, for example,in some methods the sample solution and/or wash solution are introducedthrough the top of the column and exit through the bottom end, while thedesorption solution enters and exits through the bottom opening of thecolumn. Aspiration and discharge of solution through the same end of thecolumn can be particularly advantageous in procedures designed tominimize sample loss, particularly when small volumes of liquid areused. A good example would be a procedure that employs a very smallvolume of desorption solvent, e.g., a procedure involving a highenrichment factor.

The column body can be can be composed of any material that issufficiently non-porous that it can retain fluid and that is compatiblewith the solutions, media, pumps and analytes used. A material should beemployed that does not substantially react with substances it willcontact during use of the extraction column, e.g., the sample solutions,the analyte of interest, the extraction media and desorption solvent. Awide range of suitable materials are available and known to one of skillin the art, and the choice is one of design. Various plastics make idealcolumn body materials, but other materials such as glass, ceramics ormetals could be used in some embodiments of the invention. Some examplesof preferred materials include polysulfone, polypropylene, polyethylene,polyethyleneterephthalate, polyethersulfone, polytetrafluoroethylene,cellulose acetate, cellulose acetate butyrate, acrylonitrile PVCcopolymer, polystyrene, polystyrene/acrylonitrile copolymer,polyvinylidene fluoride, glass, metal, silica, and combinations of theabove listed materials.

Some specific examples of suitable column bodies are provided in theExamples.

Extraction Media

The extraction media used in the column is preferably a form ofwater-insoluble particle (e.g, a porous or non-porous bead) that has anaffinity for an analyte of interest. Typically the analyte of interestis a protein, peptide or nucleic acid. The extraction processes can beaffinity, size exclusion, reverse phase, normal phase, ion exchange,hydrophobic interaction chromatography, or hydrophilic interactionchromatography agents. In general, the term “extraction media” is usedin a broad sense to encompass any media capable of effecting separation,either partial or complete, of an analyte from another. Thus, the terms“separation column” and “extraction column” can be used interchangeably.The term “analyte” can refer to any compound of interest, e.g., to beanalyzed or simply removed from a solution.

The bed volume of the extraction media used in the extraction columns ofthe invention is typically small, typically in the range of 0.1-1000 μL,preferably in the range of 0.1-100 μL, e.g., in a range having a lowerlimit of 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 5 or 10 μL; and an upper limit of5, 10, 15, 20, 30, 40 50, 60, 70, 80, 90, 100, 150, 200, 300, 400 or 500μL. The low bed volume contributes to a low interstitial volume of thebed, reducing the dead volume of the column, thereby facilitating therecovery of analyte in a small volume of desorption solvent.

The low bed volumes employed in certain embodiments allow for the use ofrelatively small amounts of extraction media, e.g, soft, gel-type beads.For example, some embodiments of the invention employ a bed ofextraction media having a dry weight of less than 1 gram (e.g., in therange of 0.001-1 g, 0.005-1 g, 0.01-1 g or 0.02-1 g), less than 100 mg(e.g., in the range of 0.1-100 mg, 0.5-100 mg, 1-100 mg 2-100 mg, or10-100 mg), less than 10 mg (e.g., in the range of 0.1-10 mg, 0.5-10 mg,1-10 mg or 2-10 mg), less than 2 mg (e.g., in the range of 0.1-2 mg,0.5-2 mg or 1-2 mg), or less than 1 mg (e.g., in the range of 0.1-1 mgor 0.5-1 mg).

Many of the extraction media types suitable for use in the invention areselected from a variety of classes of chromatography media. It has beenfound that many of these chromatography media types and the associatedchemistries are suited for use as solid phase extraction media in thedevices and methods of this invention.

Thus, examples of suitable extraction media include resin beads used forextraction and/or chromatography. Preferred resins include gel resins,pellicular resins, and macroporous resins.

The term “gel resin” refers to a resin comprising low-crosslinked beadmaterials that can swell in a solvent, e.g., upon hydration.Crosslinking refers to the physical linking of the polymer chains thatform the beads. The physical linking is normally accomplished through acrosslinking monomer that contains bi-polymerizing functionality so thatduring the polymerization process, the molecule can be incorporated intotwo different polymer chains. The degree of crosslinking for aparticular material can range from 0.1 to 30%, with 0.5 to 10% normallyused. 1 to 5% crosslinking is most common. A lower degree ofcrosslinking renders the bead more permeable to solvent, thus making thefunctional sites within the bead more accessible to analyte. However, alow crosslinked bead can be deformed easily, and should only be used ifthe flow of eluent through the bed is slow enough or gentle enough toprevent closing the interstitial spaces between the beads, which couldthen lead to catastrophic collapse of the bed. Higher crosslinkedmaterials swell less and may prevent access of the analytes anddesorption materials to the interior functional groups within the bead.Generally, it is desirable to use as low a level of crosslinking aspossible, so long is it is sufficient to withstand collapse of the bed.This means that in conventional gel-packed columns, slow flow rates mayhave to be used. In the present invention the back pressure is very low,and high liquid flow rates can be used without collapsing the bed.Surprisingly, using these high solvent velocities does not appear toreduce the capacity or usefulness of the bead materials. Common gelresins include agarose, sepharose, polystyrene, polyacrylate, celluloseand other substrates. Gel resins can be non-porous or micro-porousbeads.

The low back pressure associated with certain columns of the inventionresults in some cases in the columns exhibiting characteristics notnormally associated with conventional packed columns. For example, insome cases it has been observed that below a certain threshold pressuresolvent does not flow through the column. This threshold pressure can bethought of as a “bubble point.” In conventional columns, the flow ratethrough the column generally increases from zero as a smooth function ofthe pressure at which the solvent is being pushed through the column.With many of the columns of the invention, a progressively increasingpressure will not result in any flow through the column until thethreshold pressure is achieved. Once the threshold pressure is reached,the flow will start at a rate significantly greater than zero, i.e.,there is no smooth increase in flow rate with pressure, but instead asudden jump from zero to a relatively fast flow rate. Once the thresholdpressure has been exceeded flow commences, the flow rate typicallyincreases relatively smoothly with increasing pressure, as would be thecase with conventional columns.

The term “pellicular resins” refers to materials in which the functionalgroups are on the surface of the bead or in a thin layer on the surfaceof the bead. The interior of the bead is solid, usually highlycrosslinked, and usually inaccessible to the solvent and analytes.Pellicular resins generally have lower capacities than gel andmacroporous resins.

The term “macroporous resin” refers to highly crosslinked resins havinghigh surface area due to a physical porous structure that formed duringthe polymerization process. Generally an inert material (such as a solidor a liquid that does not solvate the polymer that is formed) ispolymerized with the bead and then later washed out, leaving a porousstructure. Crosslinking of macroporous materials range from 5% to 90%with perhaps a 25 to 55% crosslinking the most common materials.Macroporous resins behave similar to pellicular resins except that ineffect much more surface area is available for interaction of analytewith resin functional groups.

Examples of resins beads include polystyrene/divinylbenzene copolymers,poly methylmethacrylate, protein G beads (e.g., for IgG proteinpurification), MEP Hypercel™ beads (e.g., for IgG protein purification),affinity phase beads (e.g., for protein purification), ion exchangephase beads (e.g., for protein purification), hydrophobic interactionbeads (e.g., for protein purification), reverse phase beads (e.g., fornucleic acid or protein purification), and beads having an affinity formolecules analyzed by label-free detection. Silica beads are alsosuitable.

Soft gel resin beads, such as agarose and sepharose based beads, arefound to work surprisingly well in columns and methods of thisinvention. In conventional chromatography fast flow rates can result inbead compression, which results in increased back pressure and adverselyimpacts the ability to use these gels with faster flow rates. In thepresent invention relatively small bed volumes are used, and it appearsthat this allows for the use of high flow rates with a minimal amount ofbead compression and the problem attendant with such compression.

The average particle diameters of beads of the invention are typicallyin the range of about 1 μm to several millimeters, e.g., diameters inranges having lower limits of 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 150 μm, 200 μm, 300 μm, or 500μm, and upper limits of 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm,80 μm, 90 μm, 100 μm, 150 μm, 200 μm, 300 μm, 500 μm, 750 μm, 1 mm, 2mm, or 3 mm.

The bead size that may be used depends somewhat on the bed volume andthe cross sectional area of the column. A lower bed volume column willtolerate a smaller bead size without generating the high backpressuresthat could burst a thin membrane frit. For example a bed volume of 0.1to 1 μL bed, can tolerate 5 to 10 μm particles. Larger beds (up to about50 μL) normally have beads sizes of 30-150 μm or higher. The upper rangeof particle size is dependant on the diameter of the column bed. Thebead diameter size should not be more than 50% of the bed diameter, andpreferably less than 10% of the bed diameter.

The extraction chemistry employed in the present invention can take anyof a wide variety of forms. For example, the extraction media can beselected from, or based on, any of the extraction chemistries used insolid-phase extraction and/or chromatography, e.g., reverse-phase,normal phase, hydrophobic interaction, hydrophilic interaction,ion-exchange, thiophilic separation, hydrophobic charge induction oraffinity binding. Because the invention is particularly suited to thepurification and/or concentration of biomolecules, extraction surfacescapable of adsorbing such molecules are particularly relevant. See,e.g., SEPARATION AND SCIENCE TECHNOLOGY Vol. 2.:HANDBOOK OFBIOSEPARATIONS, edited by Satinder Ahuja, Academic Press (2000).

Affinity extractions use a technique in which a biospecific adsorbent isprepared by coupling a specific ligand (such as an enzyme, antigen, orhormone) for the analyte, (e.g., macromolecule) of interest to a solidsupport. This immobilized ligand will interact selectively withmolecules that can bind to it. Molecules that will not bind eluteunretained. The interaction is selective and reversible. The referenceslisted below show examples of the types of affinity groups that can beemployed in the practice of this invention are hereby incorporated byreference herein in their entireties. Antibody Purification Handbook,Amersham Biosciences, Edition AB, 18-1037-46 (2002); ProteinPurification Handbook, Amersham Biosciences, Edition AC, 18-1132-29(2001); Affinity Chromatography Principles and Methods, AmershamPharmacia Biotech, Edition AC, 18-1022-29 (2001); The RecombinantProtein Handbook, Amersham Pharmacia Biotech, Edition AB, 18-1142-75(2002); and Protein Purification: Principles, High Resolution Methods,and Applications, Jan-Christen Janson (Editor), Lars G. Ryden (Editor),Wiley, John & Sons, Incorporated (1989).

Examples of suitable affinity binding agents are summarized in Table I,wherein the affinity agents are from one or more of the followinginteraction categories:

-   -   1. Chelating metal—ligand interaction    -   2. Protein—Protein interaction    -   3. Organic molecule or moiety—Protein interaction    -   4. Sugar—Protein interaction    -   5. Nucleic acid—Protein interaction    -   6. Nucleic acid—nucleic acid interaction

TABLE I Examples of Affinity molecule or moiety fixed at Interactionsurface Captured biomolecule Category Ni-NTA His-tagged protein 1 Ni-NTAHis-tagged protein within a 1, 2 multi-protein complex Fe-IDAPhosphopeptides, 1 phosphoproteins Fe-IDA Phosphopeptides or 1, 2phosphoproteins within a multi-protein complex Antibody or otherProteins Protein antigen 2 Antibody or other Proteins Smallmolecule-tagged 3 protein Antibody or other Proteins Smallmolecule-tagged 2, 3 protein within a multi- protein complex Antibody orother Proteins Protein antigen within a 2 multi-protein complex Antibodyor other Proteins Epitope-tagged protein 2 Antibody or other ProteinsEpitope-tagged protein 2 within a multi-protein complex Protein A,Protein G or Antibody 2 Protein L Protein A, Protein G or Antibody 2Protein L ATP or ATP analogs; 5′- Kinases, phosphatases 3 AMP (proteinsthat requires ATP for proper function) ATP or ATP analogs; 5′- Kinase,phosphatases 2, 3 AMP within multi-protein complexes Cibacron 3G Albumin3 Heparin DNA-binding protein 4 Heparin DNA-binding proteins 2, 4 withina multi-protein complex Lectin Glycopeptide or 4 glycoprotein LectinGlycopeptide or 2, 4 glycoprotein within a multi-protein complex ssDNAor dsDNA DNA-binding protein 5 ssDNA or dsDNA DNA-binding protein 2, 5within a multi-protein complex ssDNA Complementary ssDNA 6 ssDNAComplementary RNA 6 Streptavidin/Avidin Biotinylated peptides 3 (ICAT)Streptavidin/Avidin Biotinylated engineered tag 3 fused to a protein(see avidity.com) Streptavidin/Avidin Biotinylated protein 3Streptavidin/Avidin Biotinylated protein within 2, 3 a multi-proteincomplex Streptavidin/Avidin Biotinylated engineered tag 2, 3 fused to aprotein within a multi-protein complex Streptavidin/Avidin Biotinylatednucleic acid 3 Streptavidin/Avidin Biotinylated nucleic acid 2, 3 boundto a protein or multi- protein complex Streptavidin/Avidin Biotinylatednucleic acid 3, 6 bound to a complementary nucleic acid

In one aspect of the invention an extraction media is used that containsa surface functionality that has an affinity for a protein fusion tagused for the purification of recombinant proteins. A wide variety offusion tags and corresponding affinity groups are available and can beused in the practice of the invention.

U.S. patent application Ser. No. 10/620,155 describes in detail the useof specific affinity binding reagents in solid-phase extraction.Examples of specific affinity binding agents include proteins having anaffinity for antibodies, Fc regions and/or Fab regions such as ProteinG, Protein A, Protein A/G, and Protein L; chelated metals such asmetal-NTA chelate (e.g., Nickel NTA, Copper NTA, Iron NTA, Cobalt NTA,Zinc NTA), metal-IDA chelate (e.g., Nickel IDA, Copper IDA, Iron IDA,Cobalt IDA) and metal-CMA (carboxymethylated aspartate) chelate (e.g.,Nickel CMA, Copper CMA; Iron CMA, Cobalt CMA, Zinc CMA); glutathionesurfaces-nucleotides, oligonucleotides, polynucleotides and theiranalogs (e.g., ATP); lectin surface-heparin surface-avidin orstreptavidin surface, a peptide or peptide analog (e.g., that binds to aprotease or other enzyme that acts upon polypeptides).

In some embodiments of the invention, the affinity binding reagent isone that recognizes one or more of the many affinity groups used asaffinity tags in recombinant fusion proteins. Examples of such tagsinclude poly-histidine tags (e.g., the 6X-His tag), which can beextracted using a chelated metal such as Ni-NTA-peptide sequences (suchas the FLAG epitope) that are recognized by an immobilized antibody;biotin, which can be extracted using immobilized avidin or streptavidin;“calmodulin binding peptide” (or, CBP), recognized by calmodulin chargedwith calcium-gluathione S-transferase protein (GST), recognized byimmobilized glutathione; maltose binding protein (MBP), recognized byamylose; the cellulose-binding domain tag, recognized by immobilizedcellulose; a peptide with specific affinity for S-protein (derived fromribonuclease A); and the peptide sequence tag CCxxCC (where xx is anyamino acid, such as RE), which binds to the affinity binding agentbis-arsenical fluorescein (FIAsH dye).

Antibodies can be extracted using, for example, proteins such as proteinA, protein G, protein L, hybrids of these, or by other antibodies (e.g.,an anti-IgE for purifying IgE).

Chelated metals are not only useful for purifying poly-his taggedproteins, but also other non-tagged proteins that have an intrinsicaffinity for the chelated metal, e.g., phosphopeptides andphosphoproteins.

Antibodies can also be useful for purifying non-tagged proteins to whichthey have an affinity, e.g., by using antibodies with affinity for aspecific phosphorylation site or phosphorylated amino acids.

In other embodiments of the invention extraction surfaces are employedthat are generally less specific than the affinity binding agentsdiscussed above. These extraction chemistries are still often quiteuseful. Examples include ion exchange, reversed phase, normal phase,hydrophobic interaction and hydrophilic interaction extraction orchromatography surfaces. In general, these extraction chemistries,methods of their use, appropriate solvents, etc. are well known in theart, and in particular are described in more detail in U.S. patentapplication Ser. Nos. 10/434,713 and 10/620,155, and references citedtherein, e.g., Chromatography, 5^(th) edition, PART A: FUNDAMENTALS ANDTECHNIQUES, editor: B. Heftmann, Elsevier Science Publishing Company,New York, pp A25 (1992); ADVANCED CHROMATOGRAPHIC AND ELECTROMIGRATIONMETHODS IN BIOSCIENCES, editor: Z. Deyl, Elsevier Science BV, Amsterdam,The Netherlands, pp 528 (1998); CHROMATOGRAPHY TODAY, Cohn F. Poole andSalwa K. Poole, and Elsevier Science Publishing Company, New York, pp 394 (1991); and ORGANIC SYNTHESIS ON SOLID PHASE, F. Dorwald Wiley VCHVerlag Gmbh, Weinheim 2002.

Frits

In some embodiments of the invention one or more frits is used tocontain the bed of extraction in, for example, a column. Frits can takea variety of forms, and can be constructed from a variety of materials,e.g., glass, ceramic, metal, fiber. Some embodiments of the inventionemploy frits having a low pore volume, which contribute to reducing deadvolume. The frits of the invention are porous, since it is necessary forfluid to be able to pass through the frit. The frit should havesufficient structural strength so that frit integrity can contain theextraction media in the column. It is desirable that the frit havelittle or no affinity for chemicals with which it will come into contactduring the extraction process, particularly the analyte of interest. Inmany embodiments of the invention the analyte of interest is abiomolecule, particularly a biological macromolecule. Thus in manyembodiments of the invention it desirable to use a frit that has aminimal tendency to bind or otherwise interact with biologicalmacromolecules, particularly proteins, peptides and nucleic acids.

Frits of various pores sizes and pore densities may be used provided thefree flow of liquid is possible and the beads are held in place withinthe extraction media bed.

In one embodiment, one frit (e.g., a lower frit) is bonded to andextends across the open channel of the column body. A second frit isbonded to and extends across the open channel between the bottom fritand the open upper end of the column body.

In this embodiment, the top frit, bottom frit and column body (i.e., theinner surface of the channel) define an extraction media chamber whereina bed of extraction media is positioned. The frits should be securelyattached to the column body and extend across the opening and/or openend so as to completely occlude the channel, thereby substantiallyconfining the bed of extraction media inside the extraction mediachamber. In preferred embodiments of the invention the bed of extractionmedia occupies at least 80% of the volume of the extraction mediachamber, more preferably 90%, 95%, 99%, or substantially 100% of thevolume. In some preferred embodiments the invention the space betweenthe extraction media bed and the upper and lower frits is negligible,i.e., the frits are in substantial contact with upper and lower surfacesof the extraction media bed, holding a well-packed bed of extractionmedia securely in place.

In some preferred embodiments of the invention the bottom frit islocated at the open lower end of the column body. This configuration isshown in the figures and exemplified in the Examples, but is notrequired, i.e., in some embodiments the bottom frit is located at somedistance up the column body from the open lower end. However, in view ofthe advantage the come with minimizing dead volume in the column, it isdesirable that the lower frit and extraction media chamber be located ator near the lower end. In some cases this can mean that the bottom fritis attached to the face of the open lower end, as shown in FIGS. 1-10.However, in some cases there can be some portion of the lower endextending beyond the bottom frit, as exemplified by the embodimentdepicted in FIG. 11. For the purposes of this invention, so long as thelength as this extension is such that it does not substantiallyintroduce dead volume into the extraction column or otherwise adverselyimpact the function of the column, the bottom frit is considered to belocated at the lower end of the column body. In some embodiments of theinvention the volume defined by the bottom frit, channel surface, andthe face of the open lower end (i.e., the channel volume below thebottom frit) is less than the volume of the extraction media chamber, orless than 10% of the volume of the extraction media chamber, or lessthan 1% of the volume of the extraction media chamber.

In some embodiments of the invention, the extraction media chamber ispositioned near one end of the column, which for purposes of explanationwill be described as the bottom end of the column. The area of thecolumn body channel above the extraction media chamber can be can bequite large in relation to the size of the extraction media chamber. Forexample, in some embodiments the volume of the extraction chamber isequal to less than 50%, less than 20, less than 10%, less than 5%, lessthan 2%, less than 1% or less than 0.5% of the total internal volume ofthe column body. In operation, solvent can flow through the open lowerend of the column, through the bed of extraction media and out of theextraction media chamber into the section of the channel above thechamber. For example, when the column body is a pipette tip, the openupper end can be fitted to a pipettor and a solution drawn through theextraction media and into the upper part of the channel.

The frits used in the invention are preferably characterized by having alow pore volume. Some preferred embodiments invention employ fritshaving pore volumes of less than 1 microliter (e.g., in the range of0.015-1 microliter, 0.03-1 microliter, 0.1-1 microliter or 0.5-1microliter), preferably less than 0.5 microliter (e.g., in the range of0.015-0.5 microliter, 0.03-0.5 microliter or 0.1-0.5 microliter), lessthan 0.1 microliter (e.g., in the range of 0.015-0.1 microliter or0.03-0.1 microliter) or less than 0.03 microliters (e.g., in the rangeof 0.015-0.03 microliter).

Frits of the invention preferably have pore openings or mesh openings ofa size in the range of about 5-100 μm, more preferably 10-100 μm, andstill more preferably 15-50 μm, e.g, about 43 μm. The performance of thecolumn is typically enhanced by the use of fits having pore or meshopenings sufficiently large so as to minimize the resistance to flow.The use of membrane screens as described herein typically provide thislow resistance to flow and hence better flow rates, reduced backpressure and minimal distortion of the bed of extraction media. The poreor mesh openings of course should not be so large that they are unableto adequately contain the extraction media in the chamber.

Some frits used in the practice of the invention are characterized byhaving a low pore volume relative to the interstitial volume of the bedof extraction media contained by the frit. Thus, in preferredembodiments of the invention the frit pore volume is equal to 10% orless of the interstitial volume of the bed of extraction media (e.g., inthe range 0.1-10%, 0.25-10%, 1-10% or 5-10% of the interstitial volume),more preferably 5% or less of the interstitial volume of the bed ofextraction media (e.g., in the range 0.1-5%, 0.25-5% or 1-5% of theinterstitial volume), and still more preferably 1% or less of theinterstitial volume of the bed of extraction media (e.g., in the range0.01-1%, 0.05-1% or 0.1-1% of the interstitial volume).

The pore density will allow flow of the liquid through the membrane andis preferably 10% and higher to increase the flow rate that is possibleand to reduce the time needed to process the sample.

Some embodiments of the invention employ a thin frit, preferably lessthan 350 μm in thickness (e.g., in the range of 20-350 μm, 40-350 μm, or50-350 μm), more preferably less than 200 μm in thickness (e.g., in therange of 20-200 μm, 40-200 μm, or 50-200 μm), more preferably less than100 μm in thickness (e.g., in the range of 20-100 μm, 40-100 μm, or50-100 μm), and most preferably less than 75 μm in thickness (e.g., inthe range of 20-75 μm, 40-75 μm, or 50-75 μm).

Some preferred embodiments of the invention employ a membrane screen asthe frit. The membrane screen should be strong enough to not onlycontain the extraction media in the column bed, but also to avoidbecoming detached or punctured during the actual packing of the mediainto the column bed. Membranes can be fragile, and in some embodimentsmust be contained in a framework to maintain their integrity during use.However, it is desirable to use a membrane of sufficient strength suchthat it can be used without reliance on such a framework. The membranescreen should also be flexible so that it can conform to the column bed.This flexibility is advantageous ins the packing process as it allowsthe membrane screen to conform to the bed of extraction media, resultingin a reduction in dead volume.

The membrane can be a woven or non-woven mesh of fibers that may be amesh weave, a random orientated mat of fibers i.e. a “”polymer paper,” aspun bonded mesh, an etched or “pore drilled” paper or membrane such asnuclear track etched membrane or an electrolytic mesh (see, e.g.,5,556,598). The membrane may be, e.g., polymer, glass, or metal providedthe membrane is low dead volume, allows movement of the various sampleand processing liquids through the column bed, may be attached to thecolumn body, is strong enough to withstand the bed packing process, isstrong enough to hold the column bed of beads, and does not interferewith the extraction process i.e. does not adsorb or denature the samplemolecules.

The frit can be attached to the column body by any means which resultsin a stable attachment. For example, the screen can be bonded to thecolumn body through welding or gluing. Gluing can be done with anysuitable glue, e.g., silicone, cyanoacrylate glue, epoxy glue, and thelike. The glue or weld joint must have the strength required towithstand the process of packing the bed of extraction media and tocontain the extraction media with the chamber. For glue joints, a glueshould be selected employed that does not adsorb or denature the samplemolecules.

For example, glue can be used to attach a membrane to the tip of a pipettip-based extraction column, i.e., a column wherein the column body is apipet tip. A suitable glue is applied to the end of the tip. In somecases, a rod may be inserted into the tip to prevent the glue fromspreading beyond the face of the body. After the glue is applied, thetip is brought into contact with the membrane frit, thereby attachingthe membrane to the tip. After attachment, the tip and membrane may bebrought down against a hard flat surface and rubbed in a circular motionto ensure complete attachment of the membrane to the column body. Afterdrying, the excess membrane may be trimmed from the column with a razorblade.

Alternatively, the column body can be welded to the membrane by meltingthe body into the membrane, or melting the membrane into the body, orboth. In one method, a membrane is chosen such that its meltingtemperature is higher than the melting temperature of the body. Themembrane is placed on a surface, and the body is brought down to themembrane and heated, whereby the face of the body will melt and weld themembrane to the body. The body may be heated by any of a variety ofmeans, e.g., with a hot flat surface, hot air or ultrasonically.Immediately after welding, the weld may be cooled with air or other gasto improve the likelihood that the weld does not break apart.

Alternatively, a frit can be attached by means of an annular pip, asdescribed in U.S. Pat. No. 5,833,927. This mode of attachment isparticularly suited to embodiment where the frit is a membrane screen.

The frits of the invention, e.g., a membrane screen, can be made fromany material that has the required physical properties as describedherein. Examples of suitable materials include nylon, polyester,polyamide, polycarbonate, cellulose, polyethylene, nitrocellulose,cellulose acetate, polyvinylidine difluoride, polytetrafluoroethylene(PTFE), polypropylene, polysulfone, metal and glass. A specific exampleof a membrane screen is the 43 μm pore size Spectra/Mesh® polyester meshmaterial which is available from Spectrum Labs (Ranch Dominguez, Calif.,PN 145837).

Pore size characteristics of membrane filters can be determined, forexample, by use of method #F316-30, published by ASTM International,entitled “Standard Test Methods for Pore Size Characteristics ofMembrane Filters by Bubble Point and Mean Flow Pore Test.”

The polarity of the membrane screen can be important. A hydrophilicscreen will promote contact with the bed and promote the air—liquidinterface setting up a surface tension. A hydrophobic screen would notpromote this surface tension and therefore the threshold pressures toflow would be different. A hydrophilic screen is preferred in certainembodiments of the invention.

Extraction Column Assembly

The extraction columns of the invention can be constructed by a varietyof methods using the teaching supplied herein. In some preferredembodiments the extraction column can be constructed by the engagement(i.e., attachment) of upper and lower tubular members (i.e., columnbodies) that combine to form the extraction column. Examples of thismode of column construction are described in the Examples and depictedin the figures.

In some preferred embodiments of the invention, an extraction column isconstructed by the engaging outer and inner column bodies, where eachcolumn body has two open ends (e.g., an open upper end and an open lowerend) and an open channel connecting the two open ends (e.g., a tubularbody, such as a pipette tip). The outer column body has a first frit(preferably a membrane frit) bonded to and extending across the openlower end, either at the very tip of the open end or near the open end.The section of the open channel between the open upper end and the firstfrit defines an outer column body. The inner column body likewise has afrit (preferably a membrane frit) bonded to and extending across itsopen lower end.

To construct a column according to this embodiment, an extraction mediaof interest is disposed within the lower column body, e.g., by orientingthe lower column body such that the open lower end is down and fillingor partially filling the open channel with the resin, e.g., in the formof a slurry. The inner column body, or at least some portion of theinner column body, is then inserted into the outer column body such thatthe open lower end of the inner body (where second frit is attached)enters the outer column body first. The inner column body is sealinglypositioned within the open channel of the outer column body, i.e., theouter surface of the inner column body forms a seal with the surface ofthe open. The section of the open channel between the first and secondfrits contains the extraction media, and this space defines a mediachamber. In general, it is advantageous that the volume of the mediachamber (and the volume of the bed of extraction media positioned withsaid media chamber) is less than the outer column body, since thisdifference in volume facilitates the introduction of extraction mediainto the outer column body and hence simplifies the production process.This is particularly advantageous in embodiments of the inventionwherein the extraction columns are mass produced.

In certain embodiments of the above manufacturing process, the innercolumn body is stably affixed to the outer column body by frictionalengagement with the surface of the open channel.

In some embodiments, one or both of the column bodies are tubularmembers, particularly pipette tips, sections of pipette tips or modifiedforms of pipette tips. For example, an embodiment of the inventionwherein in the two tubular members are sections of pipette tips isdepicted in FIG. 1 (FIG. 2 is an enlarged view of the open lower end andextraction media chamber of the column). This embodiment is constructedfrom a frustoconical upper tubular member 2 and a frustoconical lowertubular member 3 engaged therewith. The engaging end 6 of the lowertubular member has a tapered bore that matches the tapered externalsurfaced of the engaging end 4 of the upper tubular member, the engagingend of the lower tubular member receiving the engaging end of the uppertubular member in a telescoping relation. The tapered bore engages thetapered external surface snugly so as to form a good seal in theassembled column.

A membrane screen 10 is bonded to and extends across the tip of theengaging end of the upper tubular member and constitutes the upper fritof the extraction column. Another membrane screen 14 is bonded to andextends across the tip of the lower tubular member and constitutes thelower frit of the extraction column. The extraction media chamber 16 isdefined by the membrane screens 10 and 14 and the channel surface 18,and is packed with extraction media.

The pore volume of the membrane screens 10 and 14 is low to minimize thedead volume of the column. The sample and desorption solution can passdirectly from the vial or reservoir into the bed of extraction media.The low dead volume permits desorption of the analyte into the smallestpossible desorption volume, thereby maximizing analyte concentration.

The volume of the extraction media chamber 16 is variable and can beadjusted by changing the depth to which the upper tubular memberengaging end extends into the lower tubular member, as determined by therelative dimensions of the tapered bore and tapered external surface.

The sealing of the upper tubular member to the lower tubular in thisembodiment is achieved by the friction of a press fit, but couldalternatively be achieved by welding, gluing or similar sealing methods.

Note that in this and similar embodiments, a portion of the inner columnbody (in this case, a majority of the pipette tip 2) is not disposedwithin the first channel, but instead extends out of the outer columnbody. In this case, the open upper end of the inner column body isadapted for operable attachment to a pump, e.g., a pipettor.

FIG. 3 depicts an embodiment of the invention comprising an upper andlower tubular member engaged in a telescoping relation that does notrely on a tapered fit. Instead, in this embodiment the engaging ends 34and 35 are cyclindrical, with the outside diameter of 34 matching theinside diameter of 35, so that the concentric engaging end form a snugfit. The engaging ends are sealed through a press fit, welding, gluingor similar sealing methods. The volume of the extraction bed can bevaried by changing how far the length of the engaging end 34 extendsinto engaging end 35. Note that the diameter of the upper tubular member30 is variable, in this case it is wider at the upper open end 31 andtapers down to the narrower engaging end 34. This design allows for alarger volume in the column channel above the extraction media, therebyfacilitating the processing of larger sample volumes and wash volumes.The size and shape of the upper open end can be adapted to conform to apump used in connection with the column. For example, upper open end 31can be tapered outward to form a better friction fit with a pump such asa pipettor or syringe.

A membrane screen 40 is bonded to and extends across the tip 38 ofengaging end 34 and constitutes the upper frit of the extraction column.Another membrane screen 44 is bonded to and extends across the tip 42 ofthe lower tubular member 36 and constitutes the lower frit of theextraction column. The extraction media chamber 46 is defined by themembrane screens 40 and 44 and the open interior channel of lowertubular member 36, and is packed with extraction media.

FIG. 4 is a syringe pump embodiment of the invention with a cyclindricalbed of extraction media in the tip, and FIG. 5 is an enlargement of thetop of the syringe pump embodiment of FIG. 4. These figures show a lowdead volume column based on using a disposable syringe and column body.Instead of a pipettor, a disposable syringe is used to pump and containthe sample.

The upper portion of this embodiment constitutes a syringe pump with abarrel 50 into which a plunger 52 is positioned for movement along thecentral axis of the barrel. A manual actuator tab 54 is secured to thetop of the plunger 52. A concentric sealing ring 56 is secured to thelower end of the plunger 52. The outer surface 58 of the concentricsealing ring 56 forms a sealing engagement with the inner surface 60 ofthe barrel 50 so that movement of the plunger 52 and sealing ring 56 upor down in the barrel moves liquid up or down the barrel.

The lower end of the barrel 50 is connected to an inner cylinder 62having a projection 64 for engaging a Luer adapter. The bottom edge 66of the inner cylinder 62 has a membrane screen 68 secured thereto. Theinner cylinder 62 slides in an outer sleeve 70 with a conventional Lueradaptor 72 at its upper end. The lower segment 74 of the outer sleeve 70has a diameter smaller than the upper portion 76, outer sleeve 70forming a ledge 78 positioned for abutment with the lower end 66 andmembrane screen 68. A membrane screen 80 is secured to the lower end 82of the lower segment 74. The extraction media chamber 84 is defined bythe upper and lower membrane screens 68 and 80 and the inner channelsurface of the lower segment 74. The extraction beads are positioned inthe extraction media chamber 84. The volume of extraction media chamber84 can be adjusted by changing the length of the lower segment 74.

In other embodiments of this general method of column manufacture, theentire inner column body is disposed within the first open channel. Inthese embodiments the first open upper end is normally adapted foroperable attachment to a pump, e.g., the outer column body is a pipettetip and the pump is a pipettor. In some preferred embodiments, the outerdiameter of the inner column body tapers towards its open lower end, andthe open channel of the outer column body is tapered in the region wherethe inner column body frictionally engages the open channel, the tapersof the inner column body and open channel being complemetary to oneanother. This complementarity of taper permits the two bodies to fitsnuggly together and form a sealing attachment, such that the resultingcolumn comprises a single open channel containing the bed of extractionmedia bounded by the two frits.

FIG. 17 illustrates the construction of an example of this embodiment ofthe extraction columns of the invention. This example includes an outercolumn body 160 having a longitudinal axis 161, a central throughpassageway 162 (i.e., an open channel), an open lower end 164 for theuptake and/or expulsion of fluid, and an open upper end 166 for operableattachment to a pump, e.g., the open upper end is in communication witha pipettor or multi-channel pipettor. The communication can be direct orindirect, e.g., through one or more fittings, couplings or the like, solong as operation of the pump effects the pressure in the centralthrough passageway (referred to elsewhere herein as the “head space”).The outer column body includes a frustoconical section 168 of thethrough passageway 162, which is adjacent to the open lower end 164. Theinner diameter of the frustoconical section decreases from a first innerdiameter 170, at a position in the frustoconical section distal to theopen lower end, to a second inner diameter 172 at the open lower end. Alower frit 174, preferably a membrane screen, is bonded to and extendsacross the open lower end 164. In a preferred embodiment a membrane fritcan be bound to the outer column body by methods described herein, suchas by gluing or welding. This embodiment further includes a ring 176having an outer diameter 178 that is less than the first inner diameter170 and greater than the second inner diameter 174. An upper frit 180,preferably a membrane screen, is bonded to and extends across the ring.

To construct the column, a desired quantity of extraction media 182,preferably in the form of a slurry, is introduced into the throughpassageway through the open upper end and positioned in thefrustoconical section adjacent to the open lower end. The extractionmedia preferably forms a packed bed in contact with the lower frit 174.The ring 176 is then introduced into the through passageway through theopen upper end and positioned at a point in the frustoconical sectionwhere the inner diameter of the frustoconical section matches the outerdiameter 178 of the ring, such that the ring makes contact with andforms a seal with the surface of the through passageway. The upper frit,lower frit, and the surface of the through passageway bounded by theupper and lower frits define an extraction media chamber 184. The amountof extraction media introduced into the column is normally selected suchthat the resulting packed bed substantially fills the extraction mediachamber, preferably making contact with the upper and lower frits.

Note that the ring can take any of a number of geometries other than thesimple ring depicted in FIG. 17, so long as the ring is shaped toconform with the internal geometry of the frustoconical section andincludes a through passageway through which solution can pass. Forexample, FIG. 18 depicts a preferred embodiment wherein the ring takesthe form of a frustoconical member 190 having a central throughpassageway 192 connecting an open upper end 194 and open lower end 195.The outer diameter of the frustoconical member decreases from a firstouter diameter 196 at the open upper end to a second outer diameter 197at the open lower end. The second outer diameter 197 is greater than thesecond inner diameter 172 and less than the first inner diameter 170.The first outer diameter 196 is less than or substantially equal to thefirst inner diameter 170. An upper frit 198 is bonded to and extendsacross the open lower end 195. The frustoconical member 190 isintroduced into the through passageway of an outer column bodycontaining a bed of extraction media positioned at the lower frit 174.The tapered outer surface of the frustoconical member matches and thetaper of the frustoconical section of the open passageway, and the twosurfaces make a sealing contact. The extended frustoconicalconfiguration of this embodiment of the ring facilitates the properalignment and seating of the ring in the outer passageway.

Because of the friction fitting of the ring to the surface of thecentral through passageway, it is normally not necessary to useadditional means to bond the upper frit to the column. If desired, onecould use additional means of attachment, e.g., by bonding, gluing,welding, etc. In some embodiments, the inner surface of thefrustoconical section and/or the ring is modified to improve theconnection between the two elements, e.g., by including grooves, lockingmechanisms, etc..

In the foregoing embodiments, the ring and latitudinal cross sections ofthe frustoconical section are illustrated as circular in geometry.Alternatively, other geometries could be employed, e.g., oval, polygonalor otherwise. Whatever the geometetries, the ring and frustoconicalshapes should match to the extent required to achieve and adequatelysealing engagement. The frits are preferably, bit not necessarily,positioned in a parallel orientation with respect to one another andperpendicular to the longitudinal axis.

Other embodiments of the invention exemplifying different methods ofconstruction are also described in the examples.

Pump

In some modes of using the extraction columns of the invention, a pumpis attached to the upper open end of the column and used to aspiratedand discharge the sample from the column. The pump can take any of avariety of forms, so long as it is capable of generating a negativeinternal column pressure to aspirate a fluid into the column channelthrough the open lower end. In some preferred embodiments of theinvention the pump is also able to generate a positive internal columnpressure to discharge fluid out of the open lower end. Alternatively,other methods can be used for discharging solution from the column, e.g,centrifugation.

The pump should be capable of pumping liquid or gas, and should besufficiently strong so as to be able to draw a desired sample solution,wash solution and/or desorption solvent through the bed of extractionmedia. In order evacuate liquids from the packed bed and introduce a gassuch as air, it is desirable that the pump be able to blow or pull airthrough the column. A pump capable of generating a strong pressure willbe able to more effectively blow gas through the column, driving liquidout of the interstitial volume and contributing to a more highlypurified, concentrated analyte.

In some preferred embodiments of the invention the pump is capable ofcontrolling the volume of fluid aspirated and/or discharged from thecolumn, e.g, a pipettor. This allows for the metered intake and outtakeof solvents, which facilitates more precise elution volumes to maximizesample recovery and concentration.

Non-limiting examples of suitable pumps include a pipettor, syringe,peristaltic pump, pressurized container, centrifugal pump,electrokinetic pump, or an induction based fluidics pump. Preferredpumps have good precision, good accuracy and minimal hysteresis, canmanipulate small volumes, and can be directly or indirectly controlledby a computer or other automated means, such that the pump can be usedto aspirate, infuse and/or manipulate a predetermined volume of liquid.The required accuracy and precision of fluid manipulation will varydepending on the step in the extraction procedure, the enrichment of thebiomolecule desired, and the dimensions of the extraction column and bedvolume.

The sample solution enters the column through one end, and passesthrough the extraction bed or some portion of the entire length of theextraction bed, eventually exiting the channel through either the sameend of the column or out the other end. Introduction of the samplesolution into the column can be accomplished by any of a number oftechniques for driving or drawing liquid through a channel. Exampleswould include use of a pump (as described above) gravity, centrifugalforce, capillary action, or gas pressure to move fluid through thecolumn. The sample solution is preferably moved through the extractionbed at a flow rate that allows for adequate contact time between thesample and extraction surface. The sample solution can be passed throughthe bed more than one time, either by circulating the solution throughthe column in the same direction two or more times, or by passing thesample back and forth through the column two or more times (e.g., byoscillating a plug or series of plugs of desorption solution through thebed). In some embodiments it is important that the pump be able to pumpair, thus allowing for liquid to be blown out of the bed. Preferredpumps have good precision, good accuracy and minimal hysteresis, canmanipulate small volumes, and can be directly or indirectly controlledby a computer or other automated means, such that the pump can be usedto aspirate, infuse and/or manipulate a predetermined volume of liquid.The required accuracy and precision of fluid manipulation in the columnwill vary depending on the step in the extraction procedure, theenrichment of the biomolecule desired, and the dimensions of the column.

Solvents

Extractions of the invention typically involve the loading of analyte ina sample solution, an optional wash with a rinse solution, and elutionof the analyte into a desorption solution. The nature of these solutionswill now be described in greater detail.

With regard to the sample solution, it typically consists of the analytedissolved in a solvent in which the analyte is soluble, and in which theanalyte will bind to the extraction surface. Preferably, the binding isstrong, resulting in the binding of a substantial portion of theanalyte, and optimally substantially all of the analyte will be boundunder the loading protocol used in the procedure. The solvent shouldalso be gentle, so that the native structure and function of the analyteis retained upon desorption from the extraction surface. Typically, inthe case where the analyte is a biomolecule, the solvent is an aqueoussolution, typically containing a buffer, salt, and/or surfactants tosolubilize and stabilize the biomolecule. Examples of sample solutionsinclude cells lysates, hybridoma growth medium, cell-free translation ortranscription reaction mixtures, extracts from tissues, organs, orbiological samples, and extracts derived from biological fluids.

It is important that the sample solvent not only solubilize the analyte,but also that it is compatible with binding to the extraction phase. Forexample, where the extraction phase is based on ion exchange, the ionicstrength of the sample solution should be buffered to an appropriate pHsuch that the charge of the analyte is opposite that of the immobilizedion, and the ionic strength should be relatively low to promote theionic interaction. In the case of a normal phase extraction, the sampleloading solvent should be non-polar, e.g., hexane, toluene, or the like.Depending upon the nature of the sample and extraction process, otherconstituents might be beneficial, e.g., reducing agents, detergents,stabilizers, denaturants, chelators, metals, etc.

A wash solution, if used, should be selected such that it will removenon-desired contaminants with minimal loss or damage to the boundanalyte. The properties of the wash solution are typically intermediatebetween that of the sample and desorption solutions.

Desorption solvent can be introduced as either a stream or a plug ofsolvent. If a plug of solvent is used, a buffer plug of solvent canfollow the desorption plug so that when the sample is deposited on thetarget, a buffer is also deposited to give the deposited sample a properpH. An example of this is desorption from a protein G surface of IgGantibody which has been extracted from a hybridoma solution. In thisexample, 10 mM phosphoric acid plug at pH 2.5 is used to desorb the IgGfrom the tube. A 100 mM phosphate buffer plug at pH 7.5 follows thedesorption solvent plug to bring the deposited solution to neutral pH.The deposited material can then be analyzed, e.g., by deposition on anSPR chip.

The desorption solvent should be just strong enough to quantitativelydesorb the analyte while leaving strongly bound interfering materialsbehind. The solvents are chosen to be compatible with the analyte andthe ultimate detection method. Generally, the solvents used are knownconventional solvents. Typical solvents from which a suitable solventcan be selected include methylene chloride, acetonitrile (with orwithout small amounts of basic or acidic modifiers), methanol(containing larger amount of modifier, e.g. acetic acid ortriethylamine, or mixtures of water with either methanol oracetonitrile), ethyl acetate, chloroform, hexane, isopropanol, acetone,alkaline buffer, high ionic strength buffer, acidic buffer, strongacids, strong bases, organic mixtures with acids/bases, acidic or basicmethanol, tetrahydrofuran and water. The desorption solvent may bedifferent miscibility than the sorption solvent.

In the case where the extraction involves binding of analyte to aspecific cognate ligand molecule, e.g., an immobilized metal, thedesorption solvent can contain a molecule that will interfere with suchbinding, e.g., imidazole or a metal chelator in the case of theimmobilized metal.

Examples of suitable phases for solid phase extraction and desorptionsolvents are shown in Tables A and B.

TABLE A Desorption Normal Solvent Phase Reverse Phase Reverse PhaseFeatures Extraction Extraction Ion-Pair Extraction Typical solvent Lowto High to medium High to medium polarity range medium Typical sampleHexane, H₂O, buffers H₂O, buffers, ion- loading solvent toluene, pairingreagent CH₂CI₂ Typical Ethyl H₂O/CH₃OH, H₂O/CH₃OH, ion- desorptionacetate, H₂O/CH₃CN pairing reagent solvent acetone, (Methanol,H₂O/CH₃CN, ion- CH₃CN chloroform, acidic pairing reagent (Acetone,methanol, basic (Methanol, acetonitrile, methanol, chloroform, acidicisopropanol, tetrahydrofuran, methanol, basic methanol, acetonitrile,methanol, water, acetone, ethyl tetrahydrofuran, buffers) acetate,)acetonitrile, acetone, ethyl acetate) Sample elution Least polar Mostpolar sample Most polar sample selectivity sample components firstcomponents first components first Solvent change Increase Decreasesolvent Decrease solvent required to solvent polarity polarity desorbpolarity

TABLE B Hydrophobic Desorption Ion Exchange Interaction Affinity PhaseSolvent Features Extraction Extraction Extraction Typical solvent HighHigh High polarity range Typical sample H₂O, buffers H₂O, high salt H₂O,buffers loading solvent Typical desorption Buffers, salt solutions H₂O,low salt H₂O, buffers, pH, solvent competing reagents, heat, solventpolarity Sample elution Sample components Sample Non-binding, low-selectivity most weakly ionized components most binding, high-bindingfirst polar first Solvent change Increase ionic Decrease ionic ChangepH, add required to desorb strength or increase strength competingreagent, retained compounds change solvent pH or decrease pH polarity,increase heatII. Methods for Using the Extraction Columns

Generally the first step in an extraction procedure of the inventionwill involve introducing a sample solution containing an analyte ofinterest into a packed bed of extraction media, typically in the form ofa column as described above. The sample can be conveniently introducedinto the separation bed by pumping the solution through the column. Notethat the volume of sample solution can be much larger than the bedvolume. The sample solution can optionally be passed through the columnmore than one time, e.g., by being pumped back and forth through thebed. This can improve adsorption of analyte, which can be particularlyin cases where the analyte is of low abundance and hence maximum samplerecovery is desired.

Certain embodiments of the invention are particularly suited to theprocessing of biological samples, where the analyte of interest is abiomolecule. Of particular relevance are biological macromolecules suchas polypeptides, polynucleotides, and polysaccharides, or largecomplexes containing on or more of these moieties.

The sample solution can be any solution containing an analyte ofinterest. The invention is particularly useful for extraction andpurification of biological molecules, hence the sample solution is oftenof biological origin, e.g., a cell lysate. In one embodiment of theinvention the sample solution is a hybridoma cell culture supernatant.

One advantage of using the low bed volume columns described above isthat they allow for high linear velocity of liquid flow through thecolumn (i.e., linear flow rate) without the associated loss ofperformance and/or development of back pressure seen with moreconventional columns. High linear velocities reduce loading time.Because of the high linear velocities employed, it is likely that mostof the loading interactions are at the surface of the extractionmaterial.

The linear flow rate through a column in (cm/min) can be determined bydividing the volumetric flow (in mL/min or cm³/min) by thecross-sectional area (in cm²). This calculation implies that the columnis acting like an open tube, in that the media is being properlypenetrated by the flow of buffer/eluents. Thus, for example, the linearflow rate of a separation having a volumetric flow rate of 1 mL/minthrough a column with a cross-sectional area of 1 cm² would be (1mL/min)/(1 cm²)=1 cm/min.

An exemplary pipet tip column of the present invention might have a bedvolume of 20 μL positioned in right-angle fustrum (i.e., an invertedcone with the tip chopped off, where the bottom diameter is 1.2 mm andthe top diameter is 2.5 mm, and the approximate bed height is 8 mm). Themean diameter is about 1.8 mm, so the mean cross-sectional area of thebed is about 0.025 cm². At a flow rate of 1 mL/min, the linear flow rateis (1 mL/min)/(0.025 cm²)=40 cm/min. The mean cross-sectional area ofthe bed at the tip is about 0.011 cm², and the linear flow rate at thetip is (1 mL/min)/(0.011 cm²)=88 cm/min. It is a feature of certainextraction columns of the invention that they can be effective inmethods employing high linear flow rate exceeding flow rates previouslyused in conventional extraction methods. For example, the inventionprovides methods (and the suitable extraction columns) that employlinear flow rates of greater than 10 cm/min, 20 cm/min, 30 cm/min, 40cm/min, 50 cm/min, 60 cm/min, 70 cm/min, 80 cm/min, 90 cm/min, 100cm/min, 120 cm/min, 150 cm/min, 200 cm/min, 300 cm/min, or higher. Invarious embodiments of the invention are provided methods and columnsthat employ linear flow rate ranges having lower limits of 10 cm/min, 20cm/min, 30 cm/min, 40 cm/min, 50 cm/min, 60 cm/min, 70 cm/min, 80cm/min, 90 cm/min, 100 cm/min, 120 cm/min, 150 cm/min, or 200 cm/min;and upper limits of 50 cm/min, 60 cm/min, 70 cm/min, 80 cm/min, 90cm/min, 100 cm/min, 120 cm/min, 150 cm/min, 200 cm/min, 300 cm/min, orhigher.

Columns of the invention can accommodate a variety of flow rates, andthe invention provides methods employing a wide range of flow rates,oftentimes varying at different steps of the method. In variousembodiments, the flow rate of liquid passing through the media bed fallswithin a range having a lower limit of 0.01 mL/min, 0.05 mL/min, 0.1mL/min, 0.5 mL/min, 1 mL/min, 2 mL/min, or 4 mL/min and upper limit of0.1 mL/min, 0.5 mL/min, 1 mL/min, 2 mL/min, 4 mL/min, 6 mL/min, 10mL/min or greater. For example, some embodiments of the inventioninvolve passing a liquid though a packed bed of media having a volume ofless than 100 μL at a flow rate of between about 0.1 and about 4 mL/min,or between about 0.5 and 2 mL/min, e.g, a small packed bed of extractionmedia as described elsewhere herein. In another example, otherembodiments of the invention involve passing a liquid though a packedbed of media having a volume of less than 25 μL at a flow rate ofbetween about 0.1 and about 4 mL/min, or between about 0.5 and 2 mL/min.

In some cases, it is desirable to perform one or more steps of apurification process at a relatively slow flow rate, e.g., the loadingand/or wash steps, to maximize binding of an analyte of interest to anextraction medium. To facilitate such methods, in certain embodimentsthe invention provides a pipette comprising a body; a microprocessor; anelectrically driven actuator disposed within the body, the actuator incommunication with and controlled by the microprocessor; a displacementassembly including a displacing piston moveable within one end of adisplacement cylinder having a displacement chamber and having anotherend with an aperture, wherein said displacing piston is connected to andcontrolled by said actuator; and a pipette tip in communication withsaid aperture, wherein the microprocessor is programmable to causemovement of the piston in the cylinder at a rate that results in drawinga liquid into the pipette tip at a desired flow when the tip is incommunication with the liquid. The flow rate can be relatively slow,such as the slow flow rates described above, e.g., between about 0.1 and4 mL/min.

The pipette tip can be a pipette tip column of the invention, e.g., apipette tip comprising a tip body having an open upper end, an openlower end, and an open channel between the upper and lower ends of thetip body; a bottom flit bonded to and extending across the open channel;a top frit bonded to and extending across the open channel between thebottom frit and the open upper end of the tip body, wherein the topfrit, bottom frit, and column body define a media chamber; and a bed ofmedia positioned inside the media chamber.

In some embodiments, the microprocessor is external to the body of thepipettor, e.g., an external PC programmed to control a sample processingprocedure. In some embodiments the piston is driven by a motor, e.g., astepper motor.

The invention provides a pipettor (such as a multi-channel pipettor)suitable for acting as the pump in methods such as those describedabove. In some embodiments the pipettor comprises an electrically drivenactuator. The electrically driven actuator can be controlled by amicroprocessor, e.g., a programmable microprocessor. In variousembodiments the microprocessor can be either internal or external to thepipettor body. In certain embodiments the microprocessor is programmedto pass a pre-selected volume of solution through the bed of media at apre-selected flow rate.

The back pressure of a column will depend on the average bead size, beadsize distribution, average bed length, average cross sectional area ofthe bed, back pressure due to the frit and viscosity of flow rate of theliquid passing through the bed. For a 10 uL bed described in thisapplication, the backpressure at 2 mL/min flow rate ranged from 0.5 to 2psi. Other columns dimensions will result in backpressures ranging from,e.g., 0.1 psi to 30 psi depending on the parameters described above. Theaverage flow rate ranges from 0.05 mL/min to 10 mL/min, but willcommonly be 0.1 to 2 mL/min range with 0.2-1 mL/min flow rate being mostcommon for the 10 uL bed columns.

In some embodiments, the invention provides columns characterized bysmall bed volumes, small average cross-sectional areas, and/or lowbackpressures. This is in contrast to previously reported columns havingsmall bed volumes but having higher backpressures, e.g, for use in HPLC.Examples include backpressures under normal operating conditions (e.g.,2 mL/min in a column with 10 μL bed) less than 30 psi, less than 10 psi,less than 5 psi, less than 2 psi, less than 1 psi, less than 0.5 psi,less than 0.1 psi, less than 0.05 psi, less than 0.01 psi, less than0.005 psi, or less than 0.001 psi. Thus, some embodiments of theinvention involve ranges of backpressures extending from a lower limitof 0.001, 0.005, 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5,10 or 20 psi, to an upper limit of 0.1, 0.5, 1, 2, 3, 5, 10, 20, 30, 40,50, 60, 70, 80, 90 or 100 psi (1 psi=6.8948 kPa). An advantage of lowback pressures is there is much less tendency of soft resins, e.g.,low-crosslinked agarose or sepharose-based beads, to collapse. Becauseof the low backpressures, many of these columns can be run using onlygravity to drive solution through the column. Other technologies havinghigher backpressures need a higher pressure to drive solution through,e.g., centrifugation at relatively high speed. This limits the use ofthese types of columns to resin beads that can withstand this pressurewithout collapsing.

The term “cross-sectional area” refers to the area of a cross section ofthe bed of extraction media, i.e., a planar section of the bed generallyperpendicular to the flow of solution through the bed and parallel tothe frits. In the case of a cylindrical or frustoconical bed, the crosssection is generally circular and the cross sectional area is simply thearea of the circle (area=pi×r²). In embodiments of the invention wherethe cross sectional area varies throughout the bed, such as the case inmany of the preferred embodiments described herein having a tapered,frustoconical shape, the average cross-sectional area is an average ofthe cross sectional areas of the bed. As a good approximation, theaverage cross-sectional area of a frustoconical bed is the average ofthe circular cross-sections at each end of the bed. The averagecross-sectional area of the bed of extraction media can be quite smallin some of the columns of the invention, particularly low backpressurecolumns. Examples include cross-sectional areas of less than about 100mm², less than about 50 mm², less than about 20 mm², less than about 10mm², less than about 5 mm² or less than about 1 mm². Thus, someembodiments of the invention involve ranges of cross-sectional areasextending from a lower limit of 0.1, 0.5, 1, 2, 3, 5, 10 or 20 mm² to anupper limit of 1, 2, 3, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100mm².

After the sample solution has been introduced into the bed and analyteallowed to adsorb, the sample solution is substantially evacuated fromthe bed, leaving the bound analyte. It is not necessary that all samplesolution be evacuated from the bed, but diligence in removing thesolution can improve the purity of the final product. An optional washstep between the adsorption and desorption steps can also improve thepurity of the final product. Typically water or a buffer is used for thewash solution. The wash solution is preferably one that will, with aminimal desorption of the analyte of interest, remove excess matrixmaterials, lightly adsorbed or non-specifically adsorbed materials sothat they do not come off in the elution cycle as contaminants. The washcycle can include solvent or solvents having a specific pH, orcontaining components that promote removal of materials that interactlightly with the extraction phase. In some cases, several wash solventsmight be used in succession to remove specific material, e.g., PBSfollowed by water. These cycles can be repeated as many times asnecessary. In other cases, where light contamination can be tolerated, awash cycle can be omitted.

In some embodiments, gas is passed through the extraction bed as a meansof displacing liquid from the interstitial volume of the bed. The gascan comprise nitrogen, e.g., air or pure nitrogen. This liquid istypically made up of residual sample solution and/or wash solution. Byminimizing the presence of this unwanted solution from the bed prior tointroduction of desorption solvent, it is possible to obtain superiorpurification and concentration than could otherwise be achieved. In someembodiments of the invention this introduction of gas results in amajority of the interstitial volume being occupied by gas (i.e., free ofliquid). In some embodiments greater than 70%, 80% 90% or even 95%percent of the interstitial volume is occupied by gas. While it is oftendesirable to blow out as much free liquid from the bed as possible, itis also important in many cases to preserve the hydration of the beads,e.g., in the case of gel bead such as agarose. Preservation of beadhydration can in some cases improve the stability of bound analytes,particularly biomolecules. In these cases care should be taken to avoidexcessive drying of the bed during introduction of gas. The nature ofthe gas is not usually critical, and typically the use of air is themost convenient and economical ways of achieving the desired removal ofliquid from the bed.

The introduction of air can be concurrent with the evacuation of samplesolution and/or evacuation of wash solution from the bed. Thus, afterrunning the solution through the bed, the solution is blown out withair. In order to accomplish this most effectively, a pump should be usedthat can accurately pump liquid and that can also blow (or pull) airthrough the bed.

The volume of desorption solvent used can be very small, approximatingthe interstitial volume of the bed of extraction media. In preferredembodiments of the invention the amount of desorption solvent used isless than 10-fold greater than the interstitial volume of the bed ofextraction media, more preferably less than 5-fold greater than theinterstitial volume of the bed of extraction media, still morepreferably less than 3-fold greater than the interstitial volume of thebed of extraction media, still more preferably less than 2-fold greaterthan the interstitial volume of the bed of extraction media, and mostpreferably is equal to or less than the interstitial volume of the bedof extraction media. For example, ranges of desorption solvent volumesappropriate for use with the invention can have a lower limit of 1%, 5%,10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 150%, 200% or300% of the interstitial volume, and an upper limit of 50%, 100%, 200%,300%, 400%, 500%, 500%, 600%, 700%, 800%, or 1000% of the interstitialvolume, e.g., 10 to 200% of the interstitial volume, 20 to 100% of theinterstitial volume, 10 to 50%, 100% to 500%, 200 to 1000%, etc., of theinterstitial volume.

Alternatively, the volume of desorption solvent used can be quantifiedin terms of percent of bed volume (i.e., the total volume of media plusinterstitial space) rather than percent of interstitial volume. Forexample, ranges of desorption solvent volumes appropriate for use withthe invention can have a lower limit of 1%, 5%, 10%, 15%, 20%, 30%, 40%,50%, 60%, 70%, 80%, 90%, 100%, 150%, 200% or 300% of the bed volume, andan upper limit of 50%, 100%, 200%, 300%, 400%, 500%, 500%, 600%, 700%,800%, or 1000% of the bed volume, e.g., 10 to 200% of the bed volume, 20to 100% of the bed volume 10 to 50%, 100% to 500%, 200 to 1000%, etc.,of the bed volume.

In some embodiments of the invention, the amount of desorption solventintroduced into the column is less than 100 μL, less than 20 μL, lessthan 15 μL, less than 10 μL, less than 5 μL, or less than 1 uL. Forexample, ranges of desorption solvent volumes appropriate for use withthe invention can have a lower limit of 0.1 μL, 0.2 μL, 0.3 μL, 0.5 μL,1 μL, 2 μL, 3 μL, 5 μL, or 10 μL, and an upper limit of 2 μL, 3 μL, 5μL, 10 μL, 15 μL, 20 μL, 30 μL, 50 μL, or 100 μL, e.g., in between 1 and15 μL, 0.1 and 10 μL, or 0.1 and 2 μL.

The use of small volumes of desorption solution enables one to achievehigh enrichment factors in the described methods. The term “enrichmentfactor” as used herein is defined as the ratio of the sample volumedivided by the elution volume, assuming that there is no contribution ofliquid coming from the dead volume. To the extent that the dead volumeeither dilutes the analytes or prevents complete adsorption, theenrichment factor is reduced. For example, if 1000 μL of sample solutionis loaded onto the column and the bound analyte eluted in 10 μL ofdesorption solution, the calculated enrichment factor is 100. Note thatthe calculated enrichment factor is the maximum enrichment that can beachieved with complete capture and release of analyte. Actual achievedenrichments will typically lower due to the incomplete nature of mostbinding and release steps. Various embodiments of the invention canachieve ranges of enrichment factors having a lower limit of 1, 10, 100,or 1000, and an upper limit of 10, 100, 1000, 10,000 or 100,000.

Sometimes in order to improve recovery it is desirable to pass thedesorption solvent through the extraction bed multiple times, e.g., byrepeatedly aspirating and discharge the desorption solvent through theextraction bed and lower end of the column. Step elutions can beperformed to remove materials of interest in a sequential manner. Airmay be introduced into the bed at this point (or at any other point inthe procedure), but because of the need to control the movement of theliquid through the bed, it is not preferred.

The desorption solvent will vary depending upon the nature of theanalyte and extraction media. For example, where the analyte is ahis-tagged protein and the extraction media an IMAC resin, thedesorption solution will contain imidazole or the like to release theprotein from the resin. In some cases desorption is achieved by a changein pH or ionic strength, e.g., by using low pH or high ionic strengthdesorption solution. A suitable desorption solution can be arrived atusing available knowledge by one of skill in the art.

Extraction columns and devices of the invention should be stored underconditions that preserve the integrity of the extraction media. Forexample, columns containing agarose- or sepharose-based extraction mediashould be stored under cold conditions (e.g., 4 degrees Celsius) and inthe presence of 0.01 percent sodium azide or 20 percent ethanol. Priorto extraction, a conditioning step may be employed. This step is toensure that the tip is in a uniform ready condition, and can involvetreating with a solvent and/or removing excess liquid from the bed. Ifagarose or similar gel materials are used, the bed should be kept fullyhydrated before use.

Often it is desirable to automate the method of the invention. For thatpurpose, the subject invention provides a device for performing themethod comprising a column containing a packed bed of extraction media,a pump attached to one end of said column, and an automated means foractuating the pump.

The automated means for actuating the pump can be controlled bysoftware. This software controls the pump, and can be programmed tointroduce desired liquids into a column, as well as to evacuating theliquid by the positive introduction of gas into the column if sodesired.

For example, in certain embodiments the invention provides a generalmethod for passing liquid through a packed-bed pipette tip columncomprising the steps of:

-   -   a) providing a first column comprising:        -   i. a column body having an open upper end for communication            with a pump, a first open lower end for the uptake and            dispensing of fluid, and an open passageway between the            upper and lower ends of the column body;        -   ii. a bottom frit attached to and extending across the open            passageway;        -   iii. a top frit attached to and extending across the open            passageway between the bottom frit and the open upper end of            the column body, wherein the top frit, bottom frit, and            surface of the passageway define a media chamber;        -   iv. a first packed bed of media positioned inside the media            chamber;        -   v. a first head space defined as the section of the open            passageway between the open upper end and the top frit,            wherein the head space comprises a gas having a first head            pressure; and        -   vi. a pump sealingly attached to the open upper end, where            actuation of the pump affects the first head pressure,            thereby causing fluid to be drawn into or expelled from the            bed of media;    -   b) contacting said first open lower end with a first liquid;    -   c) actuating the pump to draw the first liquid into the first        open lower end and through the first packed bed of media; and    -   d) actuating the pump to expel at least some of the first liquid        through the first packed bed of media and out of the first open        lower end.

In certain embodiments, the invention further comprises the followingsteps subsequent to step (d):

-   -   e) contacting said first open lower end with a second liquid,        which is optionally the same as the first liquid;    -   f) actuating the pump to draw second liquid into the first open        lower end and through the first packed bed of media; and    -   g) actuating the pump to expel at least some of the second        liquid through the first packed bed of media and out of the        first open lower end.

In certain embodiments, the first head pressure of the first column isadjusted between steps (d) and (f) to render the head pressure closer toa reference pressure. For example, in certain embodiments the first headpressure of the first column is adjusted between steps (d) and (f) torender the first head pressure substantially equal to a reference headpressure. Likewise, in certain embodiments the reference head pressureis predetermined and/or is the head pressure of the first column priorto step (c).

In a number of embodiments, the above-described method further comprisethe steps of:

-   -   h) providing a second column comprising:        -   i. a column body having an open upper end for communication            with a pump, a second open lower end for the uptake and            dispensing of fluid, and an open passageway between the            upper and lower ends of the column body;        -   ii. a bottom frit attached to and extending across the open            passageway;        -   iii. a top frit attached to and extending across the open            passageway between the bottom frit and the open upper end of            the column body, wherein the top frit, bottom frit, and            surface of the passageway define a media chamber;        -   iv. a second packed bed of media positioned inside the media            chamber;        -   v. a second head space defined as the section of the open            passageway between the open upper end and the top frit,            wherein the head space comprises a gas having a second head            pressure; and        -   vi. a pump sealingly attached to the second open upper end,            where actuation of the pump affects the second head            pressure, thereby causing fluid to be drawn into or expelled            from the second packed bed of media;    -   i) contacting said second open lower end with a third liquid,        which is optionally the same as the first liquid;    -   j) actuating the pump to draw the third liquid into the second        open lower end and through the second packed bed of media;    -   k) actuating the pump to expel at least some of the third liquid        through the second packed bed of media and out of the second        open lower end.    -   l) contacting said second open lower end with a fourth liquid,        which is optionally the same as the third liquid;    -   m) actuating the pump to draw fourth liquid into the second open        lower end and through the second packed bed of media; and    -   n) actuating the pump to expel at least some of the fourth        liquid through the second packed bed of media and out of the        second open lower end, wherein the head pressure of the second        column is adjusted between steps (k) and (m) to render the head        pressure closer to a reference pressure.

In the foregoing methods, steps (b) through (g) can be performed priorto steps (i) through (n). Alternatively, steps (b) through (g) can beperformed concurrently and in parallel with steps (i) through (n). Ineither case, the reference head pressure can be the head pressure of thefirst column immediately prior to the commencement of step (f). The pumpcan be a multi-channel pipettor and the first column can be attached toa first channel of the multi-channel pipettor and the second column canbe attached to a second channel of the multi-channel pipettor. Betweensteps (d) and (f) the first head pressure can be adjusted to render thefirst and second head pressures more uniform. In some cases the methodis applied concurrently and in parallel to at least six pipette tipcolumns sealingly attached to said multi-channel pipettor, wherein eachpipette tip column comprises a head space having a head pressure, andwherein the head pressures of the at least six pipette tip columns areadjusted to render the head pressures more uniform.

In certain embodiments, the first head pressure is adjusted by breakingthe sealing attachment between the pump and the open upper end of thefirst column, exposing the head space to ambient pressure, and sealinglyreattaching the pump to the open upper end of the first column.

In certain embodiments, the second head pressure is adjusted by breakingthe sealing attachment between the pump and the open upper end of thefirst column, exposing the head space to ambient pressure, and sealinglyreattaching the pump to the open upper end of the first column.

In certain embodiments, the first column comprises a valve incommunication with the first head space, and the first head pressure isadjusted by opening this valve, thereby causing gas to enter or exit thefirst head space.

In certain embodiments, the second column comprises a valve incommunication with the second head space, and the second head pressureis adjusted by opening this valve, thereby causing gas to enter or exitthe first head space.

In certain embodiments, the first head pressure and/or second headpressure are adjusted by using the pump to cause gas to enter or exitthe head space. The first column can comprise a pressure sensor inoperative communication with said first head space, wherein saidpressure sensor is used to monitor the first head pressure and todetermine the amount of gas pumped into or from the head space. Thefirst column can comprise a first pressure sensor in operativecommunication with said first head space, a second pressure sensor inoperative communication with said second head space, which is optionallythe same as the first pressure sensor, wherein said pressure sensors areused to monitor the first and second head pressures and to determine theamount of gas pumped into or from the second head space.

The method of claim 3, wherein the first packed bed of media comprisesan interstitial space, and wherein the first head pressure is adjustedby removing bulk liquid from the interstitial space, thereby allowinggas to enter or exit the first head space through the first open lowerend and the packed bed of media.

In certain embodiments, the second packed bed of media comprises aninterstitial space, wherein the second head pressure is adjusted byremoving bulk liquid from the interstitial space, thereby allowing gasto enter or exit the second head space through the first open lower endand the packed bed of media.

In certain embodiments, throughout the method the media chamber remainssealed so as to prevent air from entering or leaving the head space. Insome cases, actuation of the pump to draw liquid into the first openlower end comprises inducing a negative head pressure that is sufficientto draw up a desired quantity of liquid but which is not so great as tocause air to enter the media chamber through the bottom frit. Forexample, in some instances the induced negative pressure ispredetermined to be sufficient to draw up a desired quantity of liquidbut not so great as to cause air to enter the media chamber through thebottom frit, e.g., a membrane frit. In some cases, after the liquid hasbeen drawn into the media chamber the outer surface of the bottom fritis in contact with air, but the air is prevented from entering ortraversing the media chamber by a surface tension that resists thepassage of gas through the membrane frit and media chamber. This can beaccomplished, for example, when the magnitude of the negative pressureis predetermined to be sufficient draw the liquid into the media chamberbut not so great as to overcome the surface tension that resists thepassage of gas through the membrane frit and media chamber. In somecases there is a surface tension that resists the initial entry of theliquid through the open lower end of the column body and into the mediachamber, and the magnitude of the negative pressure is predetermined tobe sufficient to overcome the surface tension that resists the initialentry of the liquid through the open lower end of the column body andinto the media chamber.

In some instances where throughout the method the media chamber remainssealed so as to prevent air from entering or leaving the head space,throughout the method the packed bed of media positioned inside themedia chamber comprises an interstitial space that is substantially fullof a liquid, said liquid forming the seal that prevents air fromentering or leaving the head space.

In some instances where throughout the method the media chamber remainssealed so as to prevent air from entering or leaving the head space, thestep of providing said first column comprises the steps of:

-   -   a) providing a first column comprising:        -   i. a column body having an open upper end for communication            with a pump, a first open lower end for the uptake and            dispensing of fluid, and an open passageway between the            upper and lower ends of the column body;        -   ii. a bottom frit attached to and extending across the open            passageway;        -   iii. a top frit attached to and extending across the open            passageway between the bottom frit and the open upper end of            the column body, wherein the top frit, bottom frit, and            surface of the passageway define a media chamber;        -   iv. a first packed bed of media positioned inside the media            chamber, wherein the packed bed of media comprises an            interstitial space that is substantially full of a storage            liquid, said storage liquid forming the seal that prevents            air from entering or leaving the head space; and        -   v. a first head space defined as the section of the open            passageway between the open upper end and the top frit,            wherein the head space comprises a gas having a first head            pressure; and    -   b) sealingly attaching said pump to the open upper end, wherein        after attachment to the pump the interstitial space of said bed        of media remains substantially full of storage liquid, thereby        maintaining a seal that prevents air from entering or leaving        the head space.

In certain embodiments, the storage liquid is a water miscible solventhaving a viscosity greater than that of water. In certain embodimentsthe water miscible solvent has a boiling point greater than 250° C. Thewater miscible solvent can comprise 50% of the storage liquid. In somepreferred embodiments the water miscible solvent comprises a diol,triol, or polyethylene glycol of n=2 to n=150, e.g., glycerol.

The various embodiments described above that involve adjusting orcontrolling head pressure are particularly useful in embodiments of theinvention that involve the use of automated or robotic liquid handlingsystems, e.g., automated multichannel pipettors. Thus, the variouscolumns discussed can be different columns use simultaneously on amultichannel automated system, or in some cases different columns usedsequentially on the same channel.

Multiplexing

In some embodiments of the invention a plurality of columns is run in aparallel fashion, e.g., multiplexed. This allows for the simultaneous,parallel processing of multiple samples. A description of multiplexingof extraction capillaries is provided in U.S. patent application Ser.Nos. 10/434,713 and 10/733,534, and the same general approach can beapplied to the columns and devices of the subject invention.

Multiplexing can be accomplished, for example, by arranging the columnsin parallel so that fluid can be passed through them concurrently. Whena pump is used to manipulate fluids through the column, each column inthe multiplex array can have its own pump, e.g., syringe pumps activatedby a common actuator. Alternatively, columns can be connected to acommon pump, a common vacuum device, or the like. In another example ofa multiplex arrangement, the plurality of columns is arranged in amanner such that they can be centrifuged, with fluid being driventhrough the columns by centrifugal force.

In one embodiment, sample can be arrayed from an extraction column to aplurality of predetermined locations, for example locations on a chip ormicrowells in a multi-well plate. A precise liquid processing system canbe used to dispense the desired volume of eluant at each location. Forexample, an extraction column containing bound analyte takes up 50 μl ofdesorption solvent, and 1 μL drops are spotted into microwells using arobotic system such as those commercially available from Zymark (e.g.,the SciClone sample handler), Tecan (e.g., the Genesis NPS, Aquarius orTeMo) or Cartesian Dispensing (e.g., the Honeybee benchtop system),Packard (e.g., the MiniTrak5, Evolution, Platetrack, or Apricot),Beckman (e.g., the FX-96) and Matrix (e.g., the Plate Mate 2 orSerialMate). This can be used for high-throughput assays,crystallizations, etc.

FIG. 13 depicts an example of a multiplexed extraction system. Thesystem includes a syringe holder 12 for holding a series of syringes 14(e.g., 1 mL glass syringes) and a plunger holder 16 for engaging theplungers 18 with a syringe pump 20. The syringe pump includes a screw 34to move the plunger holder and a stationary base 36. The syringe pumpcan move the plunger holder up and down while the syringe holder remainsstationary, thus simultaneously actuating all syringe plungers attachedto the holder. Each syringe includes an attachment fitting 21 forattachment of an extraction column. Attached to each syringe via thefitting is an extraction column 22. The column depicted in thisembodiment employs a modified pipet tip for the column body, membranefilters serve as the upper and lower frits 23 and 25, and the bed ofextraction media 24 is a packed bed of a gel media. The system alsoincludes a sample rack 26 with multiple positions for holding samplecollection vials 28, which can be eppendorf tubes. The sample rack isslidably mounted on two vertical rods, and the height of the rack can beadjusted by sliding it up or down the rods and locking the rack at thedesired location. The position of the rack can be adjusted to bring thelower end (the tip) of the column into contact with solution in a tubein the eppendorf rack. The system also includes a controller 30 forcontrolling the syringe pump. The controller is attached to a computer32, which can be programmed to control the movement of the pump throughthe controller. The controller allows for control of when and at whatrate the plunger rack is moved, which in turn is used to control theflow of solution through the columns, withdrawal and infusion. Controlof the plungers can be manual or automated, by means of a script filethat can be created by a user. The software allows for control of theflow rate through the columns, and an extraction protocol can includemultiple withdraw and infusion cycles, along with optional delaysbetween cycles.

In one example of a multiplexing procedure, 10 eppendorf tubescontaining a sample, e.g., 500 μL of a clarified cell lysate containinga his-tagged recombinant protein, are placed in the sample rack. One mLsyringes are attached to the syringe holder, and the plungers areengaged with the plunger holder. Extraction columns, e.g., low deadvolume packed bed columns as elsewhere herein, are affixed to thesyringe attachment fittings. The tip is conditioned by ejecting the bulkof the storage solution from the column and replacing it with air. Thesample rack is raised so that the ends of the extraction tips enter thesample. Sample solution is drawn into the columns by action of thesyringe pump, which raises the plunger holder and plungers. The pump ispreferably capable of precisely drawing up a desired volume of solutionat a desired flow rate, and of pushing and pulling solution through thecolumn. An example of a suitable syringe pump is the ME-100 (availablefrom PhyNexus, Inc., San Jose, Calif.). Control of the solvent liquid inthe column is optionally bidirectional. In this case, and where asyringe is used to control the liquid, the syringe plunger head and thesyringe body should be tightly held within the syringe pump. When thesyringe plunger direction is reversed, then there can be a delay or ahysteresis effect before the syringe can begin to move the liquid in theopposite direction. This effect becomes more important as the volumesolvent is decreased. In the ME-100 instrument, the syringe and syringeplunger are secured so that no discernable movement can be made againstthe holder rack.

If the sample volume is larger than the interstitial volume of the bed,sample is drawn through the bed and into the column body above the upperfrit. The sample solution is then expelled back into the samplecontainer. In some embodiments, the process of drawing sample throughthe bed and back out into the sample container is performed two or moretimes, each of which results in the passage of the sample through thebed twice. As discussed elsewhere herein, analyte adsorption can in somecases be improved by using a slower flow rate and/or by increasing thenumber of passages of sample through the extraction media.

The sample container is then removed and replaced with a similarcontainer holding wash solution (e.g., in the case of an immobilizedmetal extraction, 5 mM imidazole in PBS), and the wash solution ispumped back and forth through the extraction bed (as was the case withthe sample). The wash step can be repeated one or more times withadditional volumes of wash solution. A series of two or more differentwash solutions can optionally be employed, e.g., PBS followed by water.

Optionally, the syringe can be changed prior to elution. For example, 1mL disposable syringes used for sample and wash solution can be replacedwith 50 μL GasTight syringes for the elution. The original sample rack(or a different sample collection tray) is then filled with samplecollection vials (e.g., 0.5 mL Eppendorf tubes), and the height of thetubes adjusted so that the lower ends of the columns are just above thebottom of the individual samples tubes. An aliquot of desorption solventis placed at the bottom of each tube (e.g., 15 μL of 200 mM imidazolewould be typical for elution of protein off an immobilized metal columnhaving a bed volume of about 20 μL). The elution solution can bemanipulated back and forth through the bed multiple times by repeatedcycles of aspirating and expelling the solution through the column. Theelution cycle is completed by ejecting the desorption solution back intothe sample vial. The elution process can be repeated, in some casesallowing for improved sample recovery.

The above-described extraction process can be automated, for example byusing software to program the computer controller to control thepumping, e.g., the volumes, flow rates, delays, and number of cycles.

In some embodiments, the invention provides a multiplexed extractionsystem comprising a plurality of extraction columns of the invention,e.g., low dead volume pipet tip columns having small beds of packed gelresins. The system can be automated or manually operated. The system caninclude a pump or pump in operative engagement with the extractioncolumns, useful for pumping fluid through the columns in a multiplexfashion, i.e., concurrently. In some embodiments, each column isaddressable. The term “addressable” refers to the ability of the fluidmanipulation mechanism, e.g., the pumps, to individually address eachcolumn. An addressable column is one in which the flow of fluid throughthe column can be controlled independently from the flow through anyother column which may be operated in parallel. In practice, this meansthat the pumping means in at least one of the extraction steps is incontact and control of each individual column independent of all theother columns. For example, when syringe pumps are used, i.e., pumpscapable of manipulating fluid within the column by the application ofpositive or negative pressure, then separate syringes are used at eachcolumn, as opposed to a single vacuum attached to multiple syringes.Because the columns are addressable, a controlled amount of liquid canbe accurately manipulated in each column. In a non-addressable system,such as where a single pump is applied to multiple columns, the liquidhandling can be less precise. For example, if the back pressure differsbetween multiplexed columns, then the amount of liquid entering eachcolumn and/or the flow rate can vary substantially in a non-addressablesystem. Various embodiments of the invention can also include samplesracks, instrumentation for controlling fluid flow, e.g., for pumpcontrol, etc. The controller can be manually operated or operated bymeans of a computer. The computerized control is typically driven by theappropriate software, which can be programmable, e.g., by means ofuser-defined scripts.

The invention also provides software for implementing the methods of theinvention. For example, the software can be programmed to controlmanipulation of solutions and addressing of columns into sample vials,collection vials, for spotting or introduction into some analyticaldevice for further processing.

The invention also includes kits comprising one or more reagents and/orarticles for use in a process relating to solid-phase extraction, e.g.,buffers, standards, solutions, columns, sample containers, etc.

Step and Multi-dimensional Elutions

In some embodiments of the invention, desorption solvent gradients, stepelutions and/or multidimensional elutions are performed.

The use of gradients is well known in the art of chromatography, and isdescribed in detail, for example in a number of the generalchromatography references cited herein. As applied to the extractioncolumns of the invention, the basic principle involves adsorbing ananalyte to the extraction media and then eluting with a desorptionsolvent gradient. The gradient refers to the changing of at least onecharacteristic of the solvent, e.g., change in pH, ionic strength,polarity, or the concentration of some agent that influence the strengthof the binding interaction. The gradient can be with respect to theconcentration of a chemical that entity that interferes with orstabilizes an interaction, particularly a specific binding interaction.For example, where the affinity binding agent is an immobilized metalthe gradient can be in the concentration of imidazole, EDTA, etc. Insome embodiments, the result is fractionation of a sample, useful incontexts such as gel-free shotgun proteomics.

As used herein, the term “dimension” refers to some property of thedesorption solvent that is varied, e.g., pH, ionic strength, etc. Anelution scheme that involves variation of two or more dimensions, eithersimultaneously or sequentially, is referred to as a multi-dimensionalelution.

Gradients used in the context of the invention can be step elutions. Inone embodiment, two or more elution steps are performed using differentdesorption solvents (i.e., elution solvents) that vary in one or moredimensions. For example, the two or more solvents can vary in pH, ionicstrength, hydrophobicity, or the like. The volume of desorption solutionused in each dimension can be quite small, and can be passed back andforth through the bed of extraction media multiple times and at a ratethat is conducive to maximal recovery of desired analyte.

In some embodiments of the invention a multidimensional stepwise solidphase extraction is employed. This is particularly useful in theanalysis of isotope-coded affinity tagged (ICAT) peptides, as describedin U.S. patent application Ser. No. 10/434,713 and references citedtherein. A multi-dimensional extraction involves varying at least twodesorption condition dimensions.

In a typical example, a stepwise elution is performed in one dimension,collecting fractions for each change in elution conditions. For example,a stepwise increase in ionic strength could be employed where theextraction phase is based on ion exchange. The eluted fractions are thenintroduced into a second extraction column (either directly or aftercollection into an intermediate holding vessel) and in this caseseparated in another dimension, e.g., by reverse-phase, or by binding toan affinity binding group such as avidin or immobilized metal.

In some embodiments, one or more dimensions of a multidimensionalextraction are achieved by means other than an extraction column of theinvention. For example, the first dimension separation might beaccomplished using conventional chromatography, electophoresis, or thelike, and the fractions then loaded on an extraction column forseparation in another dimension.

Note that in many cases the elution of a protein will not be a simpleon-off process. That is, some desorption buffers will result in onlypartial release of analyte. The composition of the desorption buffer canbe optimized for the desired outcome, e.g., complete or near completeelution. Alternatively, when step elution is employed two or moresuccessive steps in the elution might result in incremental elution offraction of an analyte. These incremental partial elution can be usefulin characterizing the analyte, e.g., in the analysis of a multi-proteincomplex as described below.

Purification of Classes of Proteins

Extraction columns can be used to purify entire classes of proteins onthe basis of highly conserved motifs within their structure, whereby anaffinity binding agent is used that reversibly binds to the conservedmotif. For example, it is possible to immobilize particular nucleotideson the extraction media. These nucleotides include adenosine5′-triphosphate (ATP), adenosine 5′-diphosphate (ADP), adenosine5′-monophosphate (AMP), nicotinamide adenine dinucleotide (NAD), ornicotinamide adenine dinucleotide phosphate (NADP). These nucleotidescan be used for the purification of enzymes that are dependent uponthese nucleotides such as kinases, phosphatases, heat shock proteins anddehydrogenases, to name a few.

There are other affinity groups that can be immobilized on theextraction media for purification of protein classes. Lectins can beemployed for the purification of glycoproteins. Concanavilin A (Con A)and lentil lectin can be immobilized for the purification ofglycoproteins and membrane proteins, and wheat germ lectin can be usedfor the purification of glycoproteins and cells (especially T-celllymphocytes). Though it is not a lectin, the small moleculephenylboronic acid can also be immobilized and used for purification ofglycoproteins.

It is also possible to immobilize heparin, which is useful for thepurification of DNA-binding proteins (e.g. RNA polymerase I, II and III,DNA polymerase, DNA ligase). In addition, immobilized heparin can beused for purification of various coagulation proteins (e.g. antithrombinIII, Factor VII, Factor IX, Factor XI, Factor XII and XIIa, thrombin),other plasma proteins (e.g. properdin, BetaIH, Fibronectin, Lipases),lipoproteins (e.g. VLDL, LDL, VLDL apoprotein, HOLP, to name a few), andother proteins (platelet factor 4, hepatitis B surface antigen,hyaluronidase). These types of proteins are often blood and/or plasmaborne. Since there are many efforts underway to rapidly profile thelevels of these types of proteins by technologies such as protein chips,the performance of these chips will be enhanced by performing an initialpurification and enrichment of the targets prior to protein chipanalysis.

It is also possible to attach protein interaction domains to extractionmedia for purification of those proteins that are meant to interact withthat domain. One interaction domain that can be immobilized on theextraction media is the Src-homology 2 (SH2) domain that binds tospecific phosphotyrosine-containing peptide motifs within variousproteins. The SH2 domain has previously been immobilized on a resin andused as an affinity reagent for performing affinity chromatography/massspectrometry experiments for investigating in vitro phosphorylation ofepidermal growth factor receptor (EGFR) (see Christian Lombardo, et al.,Biochemistry, 34:16456 (1995)). Other than the SH2 domain, other proteininteraction domains can be immobilized for the purposes of purifyingthose proteins that possess their recognition domains. Many of theseprotein interaction domains have been described (see Tony Pawson,Protein Interaction Domains, Cell Signaling Technology Catalog, 264-279(2002)) for additional examples of these protein interaction domains).

As another class-specific affinity ligand, benzamidine can beimmobilized on the extraction media for purification of serineproteases. The dye ligand Procion Red HE-3B can be immobilized for thepurification of dehydrogenases, reductases and interferon, to name afew.

In another example, synthetic peptides, peptide analogs and/or peptidederivatives can be used to purify proteins, classes of proteins andother biomolecules that specifically recognize peptides. For example,certain classes of proteases recognize specific sequences, and classesof proteases can be purified based on their recognition of a particularpeptide-based affinity binding agent.

Multi-protein Complexes

In certain embodiments, extraction columns of the invention are used toextract and/or process multi-protein complexes. This is accomplishedtypically by employing a sample solution that is sufficientlynon-denaturing that it does not result in disruption of a proteincomplex or complexes of interest, i.e., the complex is extracted from abiological sample using a sample solution and extraction conditions thatstabilize the association between the constituents of the complex. Asused herein, the term multi-protein complex refers to a complex of twoor more proteins held together by mutually attractive chemical forces,typically non-covalent interactions. Covalent attachments wouldtypically be reversible, thus allowing for recovery of componentproteins.

In some embodiments, multi-protein complex is adsorbed to the extractionsurface and desorbed under conditions such that the integrity of thecomplex is retained throughout. That is, the product of the extractionis the intact complex, which can then be collected and stored, ordirectly analyzed (either as a complex or a mixture of proteins), forexample by any of the analytical methodologies described herein.

One example involves the use of a recombinant “bait” protein that willform complexes with its natural interaction partners. These multiproteincomplexes are then purified through a fusion tag that is attached to the“bait.” These tagged “bait” proteins can be purified through affinityreagents such as metal-chelate groups, antibodies, calmodulin, or any ofthe other surface groups employed for the purification of recombinantproteins. The identity of the cognate proteins can then be determined byany of a variety of means, such as MS.

It is also possible to purify “native” (i.e. non-recombinant) proteincomplexes without having to purify through a fusion tag. For example,this can be achieved by using as an affinity binding reagent an antibodyfor one of the proteins within the multiprotein complex. This process isoften referred to as “co-immunoprecipitation.” The multiproteincomplexes can be eluted, for example, by means of low pH buffer.

In some embodiments, the multi-protein complex is loaded onto the columnas a complex, and the entire complex or one or more constituents aredesorbed and eluted. In other embodiments, one or more complexconstituents are first adsorbed to the extraction surface, andsubsequently one or more other constituents are applied to theextraction surface, such that complex formation occurs on the extractionsurface.

In another embodiment, the extraction columns of the invention can beused as a tool to analyze the nature of the complex. For example, theprotein complex is desorbed to the extraction surface, and the state ofthe complex is then monitored as a function of solvent variation. Adesorption solvent, or series of desorption solvents, can be employedthat result in disruption of some or all of the interactions holding thecomplex together, whereby some subset of the complex is released whilethe rest remains adsorbed. The identity and state (e.g.,post-translational modifications) of the proteins released can bedetermined often, using, for example, MS. Thus, in this mannerconstituents and/or sub-complexes of a protein complex can beindividually eluted and analyzed. The nature of the desorption solventcan be adjusted to favor or disfavor interactions that hold proteincomplexes together, e.g., hydrogen bonds, ionic bonds, hydrophobicinteractions, van der Waals forces, and covalent interactions, e.g.,disulfide bridges. For example, by decreasing the polarity of adesorption solvent hydrophobic interactions will be weakened—inclusionof reducing agent (such as mercaptoethanol or dithiothrietol) willdisrupt disulfide bridges. Other solution variations would includealteration of pH, change in ionic strength, and/or the inclusion of aconstituent that specifically or non-specifically affectsprotein-protein interactions, or the interaction of a protein or proteincomplex with a non-protein biomolecule.

In one embodiment, a series of two or more desorption solvents is usedsequentially, and the eluent is monitored to determine which proteinconstituents come off at a particular solvent. In this way it ispossible to assess the strength and nature of interactions in thecomplex. For example, if a series of desorption solvents of increasingstrength is used (e.g., increasing ionic strength, decreasing polarity,changing pH, change in ionic composition, etc.), then the more looselybound proteins or sub-complexes will elute first, with more tightlybound complexes eluting only as the strength of the desorption solventis increased.

In some embodiments, at least one of the desorption solutions usedcontains an agent that effects ionic interactions. The agent can be amolecule that participates in a specific interaction between two or moreprotein constituents of a multi-protein complex, e.g., Mg-ATP promotesthe interaction and mutual binding of certain protein cognates. Otheragents that can affect protein interactions are denaturants such asurea, guanadinium chloride, and isothiocyanate, detergents such astriton X-100, chelating groups such as EDTA, etc.

In other sets of experiments, the integrity of a protein complex can beprobed through modifications (e.g., post-translational or mutations) inone or more of the proteins. Using the methods described herein theeffect of the modification upon the stability or other properties of thecomplex can be determined.

In some embodiments of the invention, multidimensional solid phaseextraction techniques, as described in more detail elsewhere herein, areemployed to analyze multiprotein complexes.

Recovery of Native Proteins

In some embodiments, the extraction devices and methods of the inventionare used to purify proteins that are functional, active and/or in theirnative state, i.e., non-denatured. This is accomplished by performingthe extraction process under non-denaturing conditions. Non-denaturingconditions encompasses the entire protein extraction process, includingthe sample solution, the wash solution (if used), the desorptionsolution, the extraction phase, and the conditions under which theextraction is accomplished. General parameters that influence proteinstability are well known in the art, and include temperature (usuallylower temperatures are preferred), pH, ionic strength, the use ofreducing agents, surfactants, elimination of protease activity,protection from physical shearing or disruption, radiation, etc. Theparticular conditions most suited for a particular protein, class ofproteins, or protein-containing composition vary somewhat from proteinto protein.

One particular aspect of the extraction technology of the invention thatfacilitates non-denaturing extraction is that the process can beaccomplished at low temperatures. In particular, because solution flowthrough the column can be done without introducing heat, e.g., withoutthe introduction of electrical current or the generation of joule heatthat typically accompanies capillary processes involving chromatographyor electroosmotic flow, the process can be carried out at lowertemperatures. Lower temperature could be room temperature, or evenlower, e.g., if the process is carried out in a cold room, or a coolingapparatus is used to cool the capillary. For example, extractions can beperformed at a temperature as low as 0° C., 2° C. or 4° C., e.g., in arange such as 1° C. to 30° C., 1° C. to 20° C., 2° C. to 30° C., 2° C.to 20° C., 4° C. to 30° C., or 4° C. to 20° C.

Another aspect of extraction as described herein that allows forpurification of native proteins is that the extraction process can becompleted quickly, thus permitting rapid separation of a protein fromproteases or other denaturing agents present in sample solution. Thespeed of the process allows for quickly getting the protein from thesample solution to the analytical device for which it is intended, or tostorage conditions that promote stability of the protein. In variousembodiments of the invention, protein extractions of the invention canbe accomplished in less than 1 minute, less than 2 minutes, less than 5minutes, less than 10 minutes, less than 15 minutes, less than 20minutes, less than 60 minutes, or less than 120 minutes.

In another aspect, extracted protein is sometimes stabilized bymaintaining it in a hydrated form during the extraction process. Forexample, if a purge step is used to remove bulk liquid (i.e., liquidsegments) from the column prior to desporption, care is taken to ensurethat gas is not blown through the bed for an excessive amount of time,thus avoiding drying out the extraction media and possibly desolvatingthe extraction phase and/or protein.

In another embodiment, the extraction process is performed underconditions that do not irreversibly denature the protein. Thus, even ifthe protein is eluted in a denatured state, the protein can be renaturedto recover native and/or functional protein. In this embodiment, theprotein is adsorbed to the extraction surface under conditions that donot irreversibly denature the protein, and eluting the protein underconditions that do not irreversibly denature the protein. The conditionsrequired to prevent irreversible denaturation are similar to those thatare non-denaturing, but in some cases the requirements are not asstringent. For example, the presence of a denaturant such as urea,isothiocyanate or guanidinium chloride can cause reversibledenaturation. The eluted protein is denatured, but native protein can berecovered using techniques known in the art, such as dialysis to removedenaturant. Likewise, certain pH conditions or ionic conditions canresult in reversible denaturation, readily reversed by altering the pHor buffer composition of the eluted protein.

The recovery of non-denatured, native, functional and/or active proteinis particularly useful as a preparative step for use in processes thatrequire the protein to be non-denatured in order for the process to besuccessful. Non-limiting examples of such processes include analyticalmethods such as binding studies, activity assays, enzyme assays, X-raycrystallography and NMR.

In another embodiment, the invention is used to stabilize RNA. This canbe accomplished by separating the RNA from some or substantially allRNAse activity, enzymatic or otherwise, that might be present in asample solution. In one example, the RNA itself is extracted and therebyseparated from RNAse in the sample. In another example, the RNaseactivity is extracted from a solution, with stabilized RNA flowingthrough the column. Extraction of RNA can be sequence specific ornon-sequence specific. Extraction of RNAse activity can be specific fora particular RNAse or class of RNAses, or can be general, e.g.,extraction of proteins or subset of proteins.

Extraction Tube as Sample Transfer Medium

In certain embodiments, an extraction column can function not only as aseparation device, but also as a means for collecting, transporting,storing and or dispensing a liquid sample.

For example, in one embodiment the extraction column is transportable,and can be readily transported from one location to another. Note thatthis concept of transportability refers to the extraction devices thatcan be easily transported, either manually or by an automated mechanism(e.g., robotics), during the extraction process. This is to bedistinguished from other systems that employ a column in a manner suchthat it is stably connected to a device that is not readily portable,e.g, n HPLC instrument. While one can certainly move such an instrument,for example when installing it in a laboratory, during use the columnremains stably attached to the stationary instrument. In contrast, incertain embodiments of the invention the column is transported.

In another embodiment, an extraction column is transportable to the sitewhere the eluted sample is destined, e.g., a storage vessel or ananalytical instrument. For example, the column, with analyte bound, canbe transported to an analytical instrument, to a chip, an arrayer, etc,and eluted directly into or onto the intended target. In one embodiment,the column is transported to an electrospray ionization chamber andeluted directly therein. In another embodiment, the column istransported to a chip or MALDI target and the analyte spotted directlyon the target.

In some embodiments of the invention involving transportable column orcolumn devices, the entire column is transported, e.g., on the end of asyringe, or just the bare column or a portion thereof.

Thus, in various embodiments the invention provides a transportableextraction device, which includes the extraction column and optionallyother associated components, e.g., pump, holder, etc. The term“transportable” refers to the ability of an operator of the extractionto transport the column, either manually or by automated means, duringthe extraction process, e.g., during sample uptake, washing, or elution,or between any of these steps. This is to be distinguished fromnon-transportable extraction devices, such as an extraction columnconnected to a stationary instrument, such that the column is nottransported, nor is it convenient to transport the column, during normaloperation.

Method for Desalting a Sample

In some embodiments, the invention is used to change the composition ofa solution in which an analyte is present. An example is the desaltingof a sample, where some or substantially all of the salt (or otherconstituent) in a sample is removed or replaced by a different salt (ornon-salt constituent). The removal of potentially interfering salt froma sample prior to analysis is important in a number of analyticaltechniques, e.g., mass spectroscopy. These processes will be generallyreferred to herein as “desalting,” with the understanding that the termcan encompass any of a wide variety of processes involving alteration ofthe solvent or solution in which an analyte is present, e.g., bufferexchange or ion replacement.

In some embodiments, desalting is accomplished by extraction of theanalyte, removal of salt, and desorption into the desired finalsolution. For example, the analyte can be adorbed in a reverse phase,ion pairing or hydrophobic interaction extraction process. In someembodiments, the process will involve use of a hydrophobic interactionextraction phase, e.g., benzyl or a reverse extraction phase, e.g., C8,C18 or polymeric. There are numerous other possibilities; e.g.,virtually any type of reverse phase found on a conventionalchromatography packing particle can be employed.

An anion exchanger can be used to adsorb an analtye, such as a proteinat a pH above its isoelectric point. Desorption can be facilitated byeluting at a pH below the isoelectric point, but this is not required,e.g., elution can be accomplished by displacement using a salt orbuffer. Likewise, a cation exchanger can be used to adsorb protein at apH below its isoelectric point, or a similar analyte.

Analytical Techniques

Extraction columns and associated methods of the invention findparticular utility in preparing samples of analyte for analysis ordetection by a variety of analytical techniques. In particular, themethods are useful for purifying an analyte, class of analytes,aggregate of analytes, etc, from a biological sample, e.g., abiomolecule originating in a biological fluid. It is particularly usefulfor use with techniques that require small volumes of pure, concentratedanalyte. In many cases, the results of these forms of analysis areimproved by increasing analyte concentration. In some embodiments of theinvention the analyte of interest is a protein, and the extractionserves to purify and concentrate the protein prior to analysis. Themethods are particular suited for use with label-free detection methodsor methods that require functional, native (i.e., non-denaturedprotein), but are generally useful for any protein or nucleic acid ofinterest.

These methods are particularly suited for application to proteomicstudies, the study of protein-protein interactions, and the like. Theelucidation of protein-protein interaction networks, preferably inconjunction with other types of data, allows assignment of cellularfunctions to novel proteins and derivation of new biological pathways.See, e.g., Curr Protein Pept Sci. 2003 4(3):159-81.

Many of the current detection and analytical methodologies can beapplied to very small sample volumes, but often require that the analytebe enriched and purified in order to achieve acceptable results.Conventional sample preparation technologies typically operate on alarger scale, resulting in waste because they produce more volume thanis required. This is particularly a problem where the amount of startingsample is limited, as is the case with many biomolecules. Theseconventional methods are generally not suited for working with the smallvolumes required for these new methodologies. For example, the use ofconventional packed bed chromatography techniques tend to require largersolvent volumes, and are not suited to working with such small samplevolumes for a number of reasons, e.g., because of loss of sample in deadvolumes, on frits, etc. See U.S. patent application Ser. No. 10/434,713for a more in-depth discussion of problems associated with previoustechnologies in connection with the enrichment and purification of lowabundance biomolecules.

In certain embodiments, the invention involves the direct analysis ofanalyte eluted from an extraction column without any intervening sampleprocessing step, e.g., concentration, desalting or the like, providedthe method is designed correctly. Thus, for example, a sample can beeluted from a column and directly analyzed by MS, SPR or the like. Thisis a distinct advantage over other sample preparation methods thatrequire concentration, desalting or other processing steps beforeanalysis. These extra steps can increase the time and complexity of theexperiment, and can result in significant sample loss, which poses amajor problem when working with low abundance analytes and smallvolumes.

One example of such an analytical technique is mass spectroscopy (MS).In application of mass spectrometry for the analysis of biomolecules,the molecules are transferred from the liquid or solid phases to gasphase and to vacuum phase. Since many biomolecules are both large andfragile (proteins being a prime example), two of the most effectivemethods for their transfer to the vacuum phase are matrix-assisted laserdesorption ionization (MALDI) or electrospray ionization (ESI). Someaspects of the use of these methods, and sample preparationrequirements, are discussed in more detail in U.S. patent applicationSer. No. 10/434,713. In general ESI is more sensitive, while MALDI isfaster. Significantly, some peptides ionize better in MALDI mode thanESI, and vice versa (Genome Technology, June 220, p 52). The extractionmethods and devices of the instant invention are particularly suited topreparing samples for MS analysis, especially biomolecule samples suchas proteins. An important advantage of the invention is that it allowsfor the preparation of an enriched sample that can be directly analyzed,without the need for intervening process steps, e.g., concentration ordesalting.

ESI is performed by mixing the sample with volatile acid and organicsolvent and infusing it through a conductive needle charged with highvoltage. The charged droplets that are sprayed (or ejected) from theneedle end are directed into the mass spectrometer, and are dried up byheat and vacuum as they fly in. After the drops dry, the remainingcharged molecules are directed by electromagnetic lenses into the massdetector and mass analyzed. In one embodiment, the eluted sample isdeposited directly from the column into an electrospray nozzle, e.g.,the column functions as the sample loader.

For MALDI, the analyte molecules (e.g., proteins) are deposited on metaltargets and co-crystallized with an organic matrix. The samples aredried and inserted into the mass spectrometer, and typically analyzedvia time-of-flight (TOF) detection. In one embodiment, the eluted sampleis deposited directly from the column onto the metal target, e.g., thecolumn itself functions as the sample loader. In one embodiment, theextracted analyte is deposited on a MALDI target, a MALDI ionizationmatrix is added, and the sample is ionized and analyzed, e.g., by TOFdetection.

In other embodiments of the invention, extraction is used in conjunctionwith other forms of MS, e.g., other ionization modes. In general, anadvantage of these methods is that they allow for the “just-in-time”purification of sample and direct introduction into the ionizingenvironment. It is important to note that the various ionization anddetection modes introduce their own constraints on the nature of thedesorption solution used, and it is important that the desorptionsolution be compatible with both. For example, the sample matrix in manyapplications must have low ionic strength, or reside within a particularpH range, etc. In ESI, salt in the sample can prevent detection bylowering the ionization or by clogging the nozzle. This problem isaddressed by presenting the analyte in low salt and/or by the use of avolatile salt. In the case of MALDI, the analyte should be in a solventcompatible with spotting on the target and with the ionization matrixemployed.

In some embodiments, the invention is used to prepare an analtye for usein an analytical method that involves the detection of a binding eventon the surface of a solid substrate. These solid substrates aregenerally referred to herein as “binding detection chips,” examples ofwhich include hybridization microarrays and various protein chips. Asused herein, the term “protein chip” is defined as a small plate orsurface upon which an array of separated, discrete protein samples (or“dots”) are to be deposited or have been deposited. In general, a chipbearing an array of discrete ligands (e.g., proteins) is designed to becontacted with a sample having one or more biomolecules which may or maynot have the capability of binding to the surface of one or more of thedots, and the occurrence or absence of such binding on each dot issubsequently determined. A reference that describes the general typesand functions of protein chips is Gavin MacBeath, Nature GeneticsSupplement, 32:526 (2002). See also Ann. Rev. Biochem., 2003 72:783-812.

In general, these methods involve the detection binding between achip-bound moiety “A” and its cognate binder “B”; i.e, detection of thereaction A+B=AB, where the formation of AB results, either directly orindirectly, in a detectable signal. Note that in this context the term“chip” can refer to any solid substrate upon which A can be immobilizedand the binding of B detected, e.g., glass, metal, plastic, ceramic,membrane, etc. In many important applications of chip technology, Aand/or B are biomolecules, e.g., DNA in DNA hybridization arrays orprotein in protein chips. Also, in many cases the chip comprises anarray multiple small, spatially-addressable spots of analyte, allowingfor the efficient simultaneous performance of multiple bindingexperiments on a small scale.

In various embodiments, it can be beneficial to process either A or B,or both, prior to use in a chip experiment, using the extraction columnsand related methodologies described herein. In general, the accuracy ofchip-based methods depends upon specific detection of the ABinteraction. However, in practice binding events other than authentic ABbinding can have the appearance of an AB binding event, skewing theresults of the analysis. For example, the presence of contaminatingnon-A species that have some affinity for B, contaminating non-B specieshaving an affinity for A, or a combination of these effects, can resultin a binding event that can be mistaken for a true AB binding event, orinterfere with the detection of a true AB binding event. These falsebinding events will throw off any measurement, and in some cases cansubstantially compromise the ability of the system to accuratelyquantify the true AB binding event.

Thus, in one embodiment, an extraction column is used to purify aprotein for spotting onto a protein chip, with the protein serving as A.In the production of protein chips, it is often desirable to spot thechip with very small volumes of protein, e.g., on the order of 1 μL, 100nL, 10 nL or even less. Many embodiments of this invention areparticularly suited to the efficient production of such small volumes ofpurified protein. The technology can also be used in a “just-in-time”purification mode, where the chip is spotted just as the protein isbeing purified.

Examples of protein analytes that can be beneficially processed by thetechnology described herein include antibodies (e.g., IgG, IgY, etc.);general affinity proteins, (e.g., scFvs, Fabs, affibodies, peptides,etc.); nucleic acids aptamers and photoaptamers as affinity molecules,and other proteins to be screened for undetermined affinitycharacteristics (e.g., protein libraries from model organisms). Thetechnology is particularly useful when applied to preparation of proteinsamples for global proteomic analysis, for example in conjunction withthe technology of Protometrix Inc. (Branford, Conn.). See, for example,Zhu et al. “Global analysis of protein activities using proteome chips(2001) Science 293(5537): 2101-05; Zhu et al., “Analysis of yeastprotein kinases using protein chips” (2000) Nature Genetics 26:1-7; andMichaud and Snyder “Proteomic approaches for the global analysis ofproteins” (2002) BioTechniques 33:1308-16.

A variety of different approaches can be used to affix A to a chipsurface, including direct/passive immobilization (can be covalent incases of native thiols associating with gold surfaces, covalentattachment to functional groups at a chip surface (e.g., self-assembledmonolayers with and without additional groups, immobilized hydrogel,etc.), non-covalent/affinity attachment to functional groups/ligands ata chip surface (e.g., Protein A or Protein G for IgGs, phenyl(di)boronicacid with salicylhydroxamic acid groups, streptavidin monolayers withbiotinylated native lysines/cysteines, etc.).

In this and related embodiments, a protein is purified and/orconcentrated using an extraction method as described herein, and thenspotted at a predetermined location on the chip. In preferredembodiments, the protein is spotted directly from an extraction columnonto the substrate. That is, the protein is extracted from a samplesolution and then eluted in a desorption solution directly onto thechip. Of course, in this embodiment it is important that the desorptionsolution be compatible with the substrate and with any chemistry used toimmobilize or affix the protein to the substrate. Typically a microarryformat involves multiple spots of protein samples (the protein samplescan all be the same or they can be different from one another). Multipleprotein samples can be spotted sequentially or simultaneously.Simultaneous spotting can be achieved by employing a multiplex format,where an array of extraction columns is used to purify and spot multipleprotein samples in parallel. The small size and portability madepossible by the use of columns facilitates the direct spotting offreshly purified samples, and also permits multiplexing formats thatwould not be possible with bulkier conventional protein extractiondevices. Particularly when very small volumes are to be spotted, it isdesirable to use a pump capable of the accurate and reproducibledispensing of small volumes of liquid, as described elsewhere herein.

In another embodiment, extraction columns of the invention are used topurify B, e.g., a protein, prior to application to a chip. As with A,purified B can be applied directly to the chip, or alternatively, it canbe collected from the column and then applied to the chip. Thedesorption solution used should be selected such that it is compatiblewith the chip, the chemistry involved in the immobilization of A, andwith the binding and/or detection reactions. As with A, the methods ofthe invention allow for “just-in-time” purification of the B molecule.

A variety of extraction chemistries and approaches can be employed inthe purification of A or B. For example, if a major contaminant orcontaminants are known and sufficiently well-defined (e.g., albumin,fibrin, etc), an extraction chemistry can be employed that specificallyremoves such contaminants. Alternatively, A or B can be trapped on theextraction surface, contaminants removed by washing, and then theanalyte released for use on the binding chip. This further allows forenrichment of the molecule, enhancing the sensitivity of the AB event.

The detection event requires some manner of A interacting with B, so thecentral player is B (since it isn't part of the protein chip itself).The means of detecting the presence of B are varied and includelabel-free detection of B interacting with A (e.g., surface plasmonresonance imaging as practiced by HTS Biosystems (Hopkinton, Mass.) orBiacore, Inc. (Piscataway, N.J.), microcantilever detection schemes aspracticed by Protiveris, Inc. (Rockville, Md.) microcalorimetry,acoustic wave sensors, atomic force microscopy, quartz crystalmicroweighing, and optical waveguide lightmode spectroscopy (OWLS),etc). Alternatively, binding can be detected by physical labeling of Binteracting with A, followed by spatial imaging of AB pair (e.g.,Cy3/Cy5 differential labeling with standard fluorescent imaging aspracticed by BD-Clontech (Palo Alto, Calif.), radioactive ATP labelingof kinase substrates with autoradiography imaging as practiced by JeriniAG (Berlin, Germany), etc), or other suitable imaging techniques.

In the case of fluorescent tagging, one can often achieve highersensitivity with planar waveguide imaging (as practiced by ZeptoSens(Witterswil, Switzerland)). See, for example, Voros et al. (2003)BioWorld 2-16-17; Duveneck et al. (2002) Analytica Chimica Acta 469:49-61, Pawlak et al. (2002) Proteomics 2:383-93; Ehrat and Kresbach(2001) Chimia 55:35-39-Weinberger et al. (2000) Pharmacogenomics395-416; Ehrat and Kresbach (2000) Chimia 54:244-46—Duveneck and Abel(1999) Review on Fluorescence-based Planar Waveguide Biosensors, Proc.SPIE, Vol. 3858: 59-71; Budachetal.(1999) Anal. Chem. 71:3347-3355;Duveneck et al. (1996) A Novel Generation of Luminescence-basedBiosensors: Single-Mode Planar Waveguide Sensors, Proc. SPIE,2928:98-109; and Neuschafer et al. (1996) Planar Waveguides as EfficientTransducers for Bioaffinity Sensors, Proc. SPIE, 2836:221-234.

Binding can also be detected by interaction of AB complex with a thirdB-specific affinity partner C, where C is capable of generating a signalby being fluorescently tagged, or is tagged with a group that allows achemical reaction to occur at that location (such as generation of afluorescent moiety, direct generation of light, etc.). Detection of thisAB-C binding event can occur via fluorescent imaging, (as practiced,e.g., by Zyomyx, Inc. (Hayward, Calif.) and SomaLogic Inc. (Boulder,Colo.)), chemiluminescence imaging (as practiced by HTS Biosystems andHypromatrix Inc (Worcester, Mass.)), fluorescent imaging via waveguidetechnology, or other suitable detection means.

In other embodiments of the invention, similar methodology is used toextract and spot other non-protein analytes in an array format, e.g.,polynucleotides, polysaccharides or natural products. Analogous to theprotein chip example above, any of these analytes can be directlyspotted on a microarray substrate, thus avoiding the necessity tocollect purified sample in some sort of vial or microwell prior totransfer to the substrate. Of course, it is also possible to use theextraction methods of the invention to purify and collect suchsubstrates prior to spotting, particularly if the high recovery andactivity to be achieved by direct spotting is not required.

In some embodiments, the technology is used to prepare a sample prior todetection by optical biosensor technology, e.g., the BIND biosensor fromSRU Biosystems (Woburn, Mass.). Various modes of this type of label-freedetection are described in the following references: B. Cunningham, P.Li, B. Lin, J. Pepper, “Colorimetric resonant reflection as a directbiochemical assay technique,” Sensors and Actuators B, Volume 81, p.316-328, Jan. 5, 2002; B. Cunningham, B. Lin, J. Qiu, P. Li, J. Pepper,B. Hugh, “A Plastic Colorimetric Resonant Optical Biosensor forMultiparallel Detection of Label-Free Biochemical Interactions,” Sensors& Actuators B, volume 85, number 3, pp 219-226, (November 2002); B. Lin,J. Qiu, J. Gerstemnaier, P. Li, H. Pien, J. Pepper, B. Cunningham, “ALabel-Free Optical Technique for Detecting Small Molecule Interactions,”Biosensors and Bioelectronics, Vol. 17, No. 9, p. 827-834, September2002; Cunningham, J. Qiu, P. Li, B. Lin, “Enhancing the SurfaceSensitivity of Colorimetric Resonant Optical Biosensors,” Sensors andActuators B, Vol. 87, No. 2, p. 365-370, December 2002, “ImprovedProteomics Technologies,” Genetic Engineering News, Volume 22, Number 6,pp 74-75, Mar. 15, 2002; and “A New Method for Label-Free Imaging ofBiomolecular Interactions,” P. Li, B. Lin, J. Gerstemnaier, and B. T.Cunningham, Accepted July, 2003, Sensors and Actuators B.

In some modes of optical biosensor technology, a colorimetric resonantdiffractive grating surface is used as a surface binding platform. Aguided mode resonant phenomenon is used to produce an optical structurethat, when illuminated with white light, is designed to reflect only asingle wavelength. When molecules are attached to the surface, thereflected wavelength (color) is shifted due to the change of the opticalpath of light that is coupled into the grating. By linking receptormolecules to the grating surface, complementary binding molecules can bedetected without the use of any kind of fluorescent probe or particlelabel. High throughput screening of pharmaceutical compound librarieswith protein targets, and microarray screening of protein-proteininteractions for proteomics are examples of applications that can beamenable to this approach.

In some embodiments, the invention is used to prepare an analyte fordetection by acoustic detection technology such as that beingcommercialized by Akubio Ltd. (Cambridge, UK). Various modes of thistype of label-free detection are described in the following references:M. A. Cooper, “Label-free screening of molecular interactions usingacoustic detection,” Drug Discovery Today 2002, 6 (12) Suppl.; M. A.Cooper “Acoustic detection of pathogens using rupture event scanning(REVS),” Directions in Science, 2002, 1, 1-2; and M. A. Cooper, F. N.Dultsev, A. Minson, C. Abell, P. Ostanin and D. Klenerman, “Direct andsensitive detection of a human virus by rupture event scanning,” NatureBiotech., 2001, 19, 833-837.

In some embodiments the invention is used to prepare an analyte fordetection by atomic force microscopy, scanning force microscopy and/ornanoarray technology such as that being commercialized by BioForceNanosciences Inc. (Ames, Iowa). See, for example, Limansky, A.,Shlyakhtenko, L. S., Schaus, S., Henderson, E. and Lyubchenko, Y.L.(2002) Amino Modified Probes for Atomic Force Microscopy, ProbeMicroscopy 2(3-4) 227-234; Kang, S-G., Henderson, E. (2002)Identification of Non-telomeric G4 binding proteins in human, E. coli,yeast and Arabidopsis. Molecules and Cells 14(3), 404-410; Clark, M. W.,Henderson, E., Henderson, W., Kristmundsdottir, A., Lynch, M., Mosher,C. and Nettikadan, S., (2001) Nanotechnology Tools for FunctionalProteomics Analysis, J. Am. Biotech. Lab; Kang, S-G., Lee, E., Schaus,S. and Henderson, E. (2001) Monitoring transfected cells withoutselection agents by using the dual-cassette expression EGFP vectors.Exp. Molec. Med. 33(3) 174-178; Lu, Q. and E. Henderson (2000) TwoTetrahymena G-DNA binding proteins, TGP I and TGP 3, have novel motifsand may play a role in micromiclear division. Nuc. Acids Res. 28(15);Mosher, C., Lynch, M., Nettikadan, S., Henderson, W., Kristmundsdottir,A., Clark, M. C. and Henderson, E., (2000) NanoArrays, The NextGeneration Molecular Array Format for High Throughput Proteomics,Diagnostics and Drug Discovery JALA, 5(5) 75-78; O'Brien, J. C., VivianW. Jones, and Marc D. Porter, Curtis L. Mosher and Eric Henderson,(2000) Immunosensing Platforms Using Spontaneously Adsorbed AntibodyFragments on Gold. Analytical Chemistry, 72(4), 703-710; Tseng, H. C.,Lu, Q., Henderson, E., and Graves, D. J., (I 999) Rescue ofphosphorylated Tau-mediated microtubule formation by a natural osinolyteTMAO. Proc Natl Acad Sci USA 1999 August 17;96(17):9503-8; Lynch, M. andHenderson, E. (1999) A reliable preparation method for imaging DNA byAFM. Microscopy Today, 99-9, 10; Mazzola, L. T., Frank, C. W., Fodor, S.P. A., Lu, Q., Mosher, C., Lartius, R. and Henderson, E. (1999)Discrimination of DNA hybridization using chemical force microscopy.Biophys. J., 76, 2922-2933; Jones, V. W., Kenseth, J. R., Porter, M. D.,Mosher, C. L. and Henderson, E. (1998) Microminiaturized immunoassaysusing Atomic Force Microscopy and compositionally patterned antigenarrays. Analy. Chem., 70 (7), 123 3-124 1; Fritzsche, W. and Henderson,E. (1997) Ribosome substructure investigated by scanning forcemicroscopy and image processing. J. Micros. 189, 50-56; Fritzsche, W.and Henderson, E. (1997) Mapping elasticity of rehydrated metaphasechromosomes by scanning force microscopy. Ultramicroscopy 69 (1997),191-200; Schaus, S. S. and Henderson, E. (1997) Cell viability andprobe-cell membrane interactions of XR1 glial cells imaged by AFM.Biophysical Journal, 73, 1205-1214-W. Fritzsche, J. Symanzik, K.Sokolov, E. Henderson (1997) Methanol induced lateral diffusion ofcolloidal silver particles on a silanized glass surface—a scanning forcemicroscopy study. Journal of Colloidal and Interface Science, Journal ofColloid and Interface Science 185 (2), 466-472-Fritzsche, W andHenderson, E. (1997) Chicken erythrocyte nucleosomes have a definedorientation along the linker DNA—a scanning force microscopy study.Scanning 19, 42-47; W. Fritzsche, E. Henderson (1997) Scanning forcemicroscopy reveals ellipsoid shape of chicken erythrocyte nucleosomes.Scanning 19, 42-47; Vesekna, J., Marsh, T., Miller, R., Henderson, E.(1996) Atomic force microscopy reconstruction of G-wire DNA. J. Vac.Sci. Technol. B 14(2), 1413-1417; W. Fritzsche, L. Martin, D. Dobbs, D.Jondle, R. Miller, J. Vesenka, E. Henderson (1996) Reconstruction ofRibosomal Subunits and rDNA Chromatin Imaged by Scanning ForceMicroscopy. Journal of Vacuum Science and Technology B 14 (2),1404-1409-Fritzsche, W. and Henderson, E. (1996) Volume determination ofhuman metaphase chromosomes by scanning force microscopy. ScanningMicroscopy 10(1); Fritzsche, W., Sokolov, K., Chumanov, G., Cottom, T.M. and Henderson, E. (1996) Ultrastructural characterization ofcolloidal metal films for bioanalytical applications by SFM. J. Vac.Sci. Technol., A 14 (3) (1996), 1766-1769; Fritzsche, W., Vesenka, J.and Henderson, E. (1995) Scanning force microscopy of chromatin.Scanning Microscopy. 9(3), 729-739; Vesenka, J., Mosher, C. Schaus, S.Ambrosio, L. and Henderson, E. (1995) Combining optical and atomic forcemicroscopy for life sciences research. BioTechniques, 19, 240-253;Jondle, D. M., Ambrosio, L., Vesenka, J. and Henderson, E. (1995)Imaging and manipulating chromosomes with the atomic force microscope.Chromosome Res. 3 (4), 23 9-244; Marsh, T. C., J. Vesenka, and E.Henderson. (1995) A new DNA nanostructure imaged by scanning probemicroscopy. Nuc. Acids Res., 23(4), 696-700; Martin, L. D., J. P.Vesenka, E. R. Henderson, and D. L. Dobbs. (1995) Visualization ofnucleosomal structure in native chromatin by atomic force microscopy.Biochemistry, 34,4610-4616—Mosher, C., Jondle, D., Ambrosio, L.,Vesenka, J. and Henderson, E. (1994) Microdissection and Measurement ofPolytene Chromosomes Using the Atomic Force Microscope. ScanningMicroscopy, 8(3) 491-497; Vesenka, J., R. Miller, and E. Henderson.(1994) Three-dimensional probe reconstruction for atomic forcemicroscopy. Rev. Sci. Instrum., 65, 1-3—Vesenka, J., Manne, S.,Giberson, R., Marsh, T. and Henderson, E. (1993) Colloidal goldparticles as an incompressible atomic force microscope imaging standardfor assessing the compressibility of biomolecules., Biophys. J., 65,992-997; Vesenka, J., S. Manne, G. Yang, C. J. Bustamante and E.Henderson. (1993) Humidity effects on atomic force microscopy ofgold-labeled DNA on mica. Scan. Mic. 7(3): 781-788; Rubim, J. C., Kim,J-H., Henderson, E. and Cotton, T. M. (1993) Surface enhanced ramanscattering and atomic force microscopy of brass electrodes in sulfuricacid solution containing benzotriazole and chloride ion. AppliedSpectroscopy 47(1), 80-84; Parpura, V., Haydon, P. G., Sakaguchi, D. S.,Henderson, E. (1993) Atomic force microscopy and manipulation of livingglial cells. J. Vac. Sci. Technol. A, I 1 (4), 773-775; Shaiu, W-L.,Larson, D. D., Vesenka, J. Henderson, E. (1993) Atomic force microscopyof oriented linear DNA molecules labeled with 5 nm gold spheres. Nuc.Acids Res., 21 (1) 99-103; Henderson, E., Sakaguchi, D. S. (1993)Imaging F-Actin in fixed glial cells with a combined opticalfluorescence/atomic force microscope. Neurohnage 1, 145-150; Parpura, V.Haydon, P. G. and Henderson, E. (1993) Three-dimensional imaging ofneuronal growth cones and glia with the Atomic Force Microscope. J. CellSci. 104, 427-43 2; Henderson, E., Haydon, P. G and Sakaguchi, D. A.(1992) Actin filaments dynamics in living glial cells imaged by atomicforce microscopy. Science, 25 7, 1944-1946; Henderson, E. (1992) Atomicforce microscopy of conventional and unconventional nucleic acidStructures. J. Microscopy, 167, 77-84—Henderson, E. (1992)Nanodissection of supercoiled plasmid DNA by atomic force microscopy.Nucleic Acids Research, 20 (3) 445-447.

In some embodiments the invention is used to prepare an analyte fordetection by a technology involving activity-based protein profilingsuch as that being commercialized by ActivX, Inc. (La Jolla, Calif.).Various modes of this methodology are described in the followingreferences: Kidd et al. (2001) Biochemistry 40:4005-4015; Adam etal.(2000) Chemistry and Biiology 57:1-16; Liu et al. (1999) PNAS96(26):146940-14699; Cravatt and Sorensen (2000) Curr. Opin. Chem. Biol.4:663-668; Patricelli et al. (2001) Proteomics 1-1067-71.

In some embodiments the invention is used to prepare an analyte foranalysis by a technology involving a kinetic exclusion assay, such asthat being commercialized by Sapidyne Instruments Inc. (Boise, Id.).See, e.g., Glass, T. (1995) Biomedical Products 20(9): 122-23; andOhumura et al. (2001) Analytical Chemistry 73 (14):3 3 92-99.

In some embodiments, the systems and methods of the invention are usefulfor preparing protein samples for crystallization, particularly for usein X-ray crystallography -based protein structure determination. Theinvention is particularly suited for preparation of samples for use inconnection with high throughput protein crystallization methods. Thesemethods typically require small volumes of relatively concentrated andpure protein, e.g., on the order of 1 μL, per crystallization conditiontested. Instrumentation and reagents for performing high throughputcrystallization are available, for example, from Hampton Research Corp.(Alison Viejo, Calif.), Robotizing International Inc. (Carlsbad,Calif.), Genomic Solutions, Inc. (Ann Arbor, Mich.) and Corning LifeSciences (Kennebunk, Me.). Typically, protein crystallization involvesmixing the protein with a mother liquor to form a protein drop, and thenmonitoring the drop to see if suitable crystals form, e.g., the sittingdrop or hanging drop methods. Since the determination of appropriatecrystallization conditions is still largely empirical, normally aprotein is tested for crystallization under a large number of differentconditions, e.g., a number of different candidate mother liquors areused. The protein can be purified by extraction prior to mixture withmother liquor. The sample can be collected in an intermediate holdingvessel, from which it is then transferred to a well and mixed withmother liquor. Alternatively, the protein drop can be dispensed directlyfrom the column to a well. The invention is particularly suited for usein a high-throughput mode, where drops of protein sample are introducedinto a number of wells, e.g., the wells of a multi-well plate (e.g., 94,384 wells, etc.) such as a Crystallex 384 plate from Corning (CorningLife Sciences, Kennebunk Me.). The protein drops and/or mother liquorscan be dispensed into microwells using a high precision liquiddispensing system such as the Cartesian. Dispensing System Honeybee(Genomic Solutions, Inc., Ann Arbor, Mich.). In high throughput modes itis desirable to automate the process of crystals trial analysis, usingfor example a high throughput crystal imager such as the Rob MicroscopeIII (Robotizing International Inc., Carlsbad, Calif.).

Other analytical techniques particularly suited for use in conjunctionwith certain embodiments of the invention include surface immobilizedassays, immunological assays, various ligand displacement/competitionassays, direct genetic tests, biophysical methods, direct forcemeasurements, NMR, electron microscopy (including cryo-EM),microcalorimetry, mass spectroscopy, IR and other methods such as thosediscussed in the context of binding detection chips, but which can alsobe used in non-chips contexts.

In one embodiment, an extracted sample is eluted in a deuterateddesorption solvent (i.e., D₂0, chloroform-d, etc.) for direct analysisby NMR, e.g., an integrated microfluidic-NMR system. For example, abiomolecule analyte is extracted, washed with PBS or a similar reagent,washed with water as needed, and then liquid blown out. The column isthen washed with D₂0, e.g, one or more small slugs of D₂0, so as toreplace substantially all of the water in the extraction phase matrixwith D₂0. The analyte is then eluted with a deuterated desorptionsolution, e.g., a buffer made up in D₂0. Deuterated solvents can beobtained, e.g., from Norell, Inc. (Landisville, N.J.).

In general, it is important to use a desorption solvent that isconsistent with the requirements of the analytical method to beemployed, e.g., in many cases it is preferable that the pH of thedesorption solvent be around neutral, such as for use with some proteinchips.

Adjustment and Control of Column Head Pressure

Various embodiments of the invention employ packed-bed pipette tipcolumns of the following format, as illustrated in FIG. 15. The columnsemploy a pipette tip or modified pipette tip as a column body. Thecolumn body has an open upper end 202 for communication with a pump 204(e.g., a pipettor, or a channel of a multi-channel pipettor, attached tothe open upper end by a sealing fitting), an open lower end 206 for theuptake and dispensing of fluid, and an open passageway between the upperand lower ends of the column body. A bottom frit 210 is attached to andextends across the open passageway. In the illustration the bottom fritis positioned at the open lower end itself, i.e., at the lower terminusof the column body. While this positioning is preferred in many cases,in alternative embodiments the frit could be attached at a positionspanning the open passageway at some distance from the terminus or openlower end. As a result of the positioning and attachment of the frit,substantially any liquid entering or exiting the open passageway via theopen lower end will pass through the frit.

The column further includes a top frit 212 that is attached to andextends across the open passageway between the bottom frit 210 and theopen upper end 202. The top frit, bottom frit and the surface of theopen passageway define a media chamber 216 that contains a packed bed ofmedia, e.g., a packed bed of extraction media having an affinity for ananalyte of interest. The column further includes a head space 208,defined as the section of the open passageway between the upper open endand the pump fitting 214. In a typical embodiment of the invention, thevolume of the head space is substantially greater than the volume of themedia chamber. The head space is open and can accommodate liquid and/orgas that enters through the open lower end and media chamber.

The passage of fluid through the bed of extraction media is controlledby means of the pump 204. The pump is sealing attached to the open upper202, i.e., a seal is formed between the pump fitting 214 and the openupper end, such that the pump is able to pump gas into or out of thehead space, thereby affecting the pressure in the head space, i.e., thehead pressure. In alternate embodiments, the attachment of the openupper end to the pump can be direct or indirect, e.g., the attachmentcan be through valves, fittings, hoses, etc., so long as the attachmentis operative and actuation of the pump affects the head pressure,thereby causing fluid to be drawn into or expelled from the bed ofmedia.

In some embodiments of the invention, the column and pump combinationillustrated in FIG. 15 is used to pass a liquid back and forth throughthe packed bed of media. The open lower end is brought into contact withthe liquid, and the pump is actuated to draw the liquid into the loweropen end and through the packed bed of media, i.e., by generation of anegative pressure in the head space relative to the ambient pressure. Inmany embodiments, the volume of liquid is substantially greater than theinterstitial volume of the bed of extraction media. The liquid passesthrough the bed and accumulates in the head space. The pump is thenactuated to expel all or some of the liquid through the bed of media andout the open lower end, i.e., by generation of a positive pressure inthe head space relative to the ambient pressure, e.g., atmosphericpressure. This process is typically repeated multiple times with aplurality of different liquids, e.g. a sample solution containing ananalyte of interest, wash solution(s), and desorption solution, in anyof the various processes described herein.

The term “ambient pressure” refers to the air pressure outside thecolumn, normally atmospheric air pressure, or the pressure of liquid incontact with the open lower end to be pumped through the media. Duringthe process of pumping liquid through the bed of media, the headpressure will at times differ from the ambient pressure. This occursbecause the sealing attachment to the pump at the upper open end and thebed of extraction media and frits at the lower open end impede the flowof gas into and out of the head space. This is particularly the casewhen the interstitial space of the bed of media is filled with liquidand/or when the frit is wet.

For example, in order to draw a liquid through the lower frit and intothe bed of extraction media the pump is used to draw air from the headspace, thereby generating a relative negative head pressure. Once thehead pressure becomes sufficiently negative relative to the ambientpressure, liquid will be drawn up through the open upper end. Liquidflow is resisted by the backpressure of the column and by surfacetension effects within the column, particularly in the bed and at theinterface of the bed and frits. Surface tension can arise from theinteraction of liquid with the packed bed of media and/or with the frit.This surface tension results in an initial resistance to flow of liquidthrough the bed of extraction media, described elsewhere herein as aform of “bubble point.” As a result, a certain minimum threshold ofnegative head pressure must be generated before liquid will commenceflowing through the bed. In addition, there is the backpressure of thecolumn that must be overcome in order for liquid to flow through thebed. Thus, in operation of the column a sufficiently negative headpressure must be generated to overcome backpressure and surface tensioneffects prior to flow commencing through the bed. As a result,significant negative head pressures can develop and be maintained; themagnitude of the head pressure will to some extent depend upon thebackpressure and surface tension, which in turn depends upon the size ofthe bed, the nature of the media, the nature of the packing, the natureof the frits, and the interaction of the frits with the bed.

Likewise, a relatively positive head pressure is generated in order toexpel liquid from the column. Expulsion of liquid from the column isresisted by the same backpressure and surface tension effects describedfor liquid uptake. As a result, relatively large positive head pressurescan be generated and maintained by the sealing attachment at the upperopen end and the resistance to gas flow provided by the bed and frits.

During the course of performing a purification using the columns of theinvention, the head pressure of any given column will vary during thecourse of the process. For example, let us consider an embodiment wheremultiple pipette tip columns and a programmable multi-channel pipettorare used. The columns are frictionally attached to fittings on thepipettor, which can result in an initial positive pressure in the headspace. This positive pressure is the result of compression of the headspace as the column is pushed further onto the fitting after forming aseal between the upper open end and the fitting. This positive pressurecan be maintained for a substantial period of time, since the seal andthe backpressure and surface tension of the bed inhibit the exit of gasfrom the head space.

In order to draw liquid into the bed, the pump is used draw gas from thehead space, thereby generating a head pressure sufficiently negative toovercome backpressure and surface tension effects. This will generate arelatively stable negative pressure. To expel the liquid, the pump isused to force gas into the head space, thereby generating a headpressure sufficiently positive to overcome backpressure and surfacetension effects. This process is repeated through each cycle of drawingand expelling liquid from the column, and the process is accompanied bya cycle of negative and positive head pressures.

Note that the head pressure at the beginning of each pumping step isgenerally not neutral or ambient pressure, but is instead a negative orpositive pressure resulting from a prior pumping step, or from theattachment of the tip to the pipettor, or the like. For example,consider a typical purification procedure that involves passing ananalyte-containing solution through an extraction bed, followed by awash and finally a desorption step. At the outset of the desorptionstep, there will generally be a non-neutral pressure, e.g., a positivehead pressure residual from the last step of expelling wash solution.The magnitude of this positive head pressure is the cumulative result ofall the previous steps, and will depend to some extent upon the natureof the particular tip column. For example, the greater the resistance toflow that must be overcome by the pump (i.e., the backpressure andsurface tension of the particular column), the greater the positivepressure that must be generated in the head space to expel liquid fromthe column. In order to draw desorption liquid into the bed, the pumpmust draw enough gas from the head space to compensate for the positivepressure and create a negative head pressure sufficient to draw thedesired amount of desorption solution through the bed.

FIG. 16 depicts the relationship between head pressure and pump andliquid movement in a typical extraction process. This particular plotrepresents an initial expulsion of liquid out of the column and then onecycle of uptake and expulsion of liquid from the column. The x-axis istime, and the y-axis is pressure or volume. The solid line at the toprepresents head pressure as a function of time, the dashed linerepresents displacement of a pipettor (in this case a syringe), and thedotted line at the bottom represents the volume of liquid in a pipettetip column. A syringe is being used as the pump; movement of the syringeplunger causes a change in the volume of the syringe chamber, which isfilled with air and sealingly connected to the open upper end of a tipcolumn as depicted in FIG. 15. At time zero, the volume of liquid (e.g.,aqueous solution) in the tip is about 60 uL, the volume of the syringechamber is about 160 uL, and the head pressure is about +10 inches ofwater. As the syringe plunger is depressed, the volume of the syringechamber decreases, which causes the positive head pressure to increase.This increase in head pressure causes the liquid to be expelled from theopen lower end of the column, resulting in a decrease in the volume ofliquid in the column. As the volume of liquid in the tip approacheszero, the head pressure begins to fluctuate. At this point, little ifany liquid is leaving the bed, but there is still some liquid remainingin the interstitial space of the bed. The interaction of this liquidwith the bed and frits results in a surface tension effect that impedesthe flow of air through the bed. As the volume of the syringe chambercontinues to decrease, the increasing positive head pressure willeventually force air through the bed in the form of air bubbles. Thesurface tension in the bed resists movement of the air bubbles throughthe bed, but air bubbles will be ejected once sufficient positive headpressure is achieved. The passage of each air bubble through the bed andout of the column will result in a decrease in the head pressure. Theresult is large fluctuations in the head pressure as the syringe plungeris depressed under these conditions; the head volume builds up as thesyringe chamber volume decreases, but with each air bubble expelledthrough the bed the head pressure will decrease. In many cases dramaticfluctuations in head pressure are observed, as depicted in FIG. 16between times 1 and 2 (1 and 2 minutes). Each spike represents the headpressure at which an air bubble was forced out of the column.

At time 2 the volume of the syringe chamber is zero, and the plunger isnow retracted, resulting in the increase of the syringe chamber volumewith time. The increasing syringe chamber volume translates intodecreasing head pressure, eventually resulting in a negative headpressure at a time of about 2.5. Once the head pressure is sufficientlynegative to overcome the surface tension and backpressure effects liquidstarts flowing through the bed and back into the head space. At time 4the plunger stops moving and the syringe chamber volume has reached itsmaximum. Liquid stops flowing into the tip, and the head pressuresstabilizes at a constant, moderately low pressure.

Starting at time 6, the plunger is again depressed, resulting in anincrease in head pressure up to a pressure that is sufficiently positivethat liquid begins flowing out of the tip. Note that some head pressureresults from the weight of the liquid above the bed in the head space,and this can contribute to the pressure that is being applied to expelthe liquid. Between time points 7.5 and 8 all of the bulk of the liquidis ejected from the column, and the head pressure rises againdramatically due to the backpressure and surface tension effectsdescribed earlier, i.e., as in the conditions between 1 and 2 minutes.

In certain embodiments of the invention, it is desirable to adjust thehead pressure prior to or during the course of a purification process,e.g., prior to a pumping step. Adjustment of the head pressure isparticularly important in automated processes, e.g., processes involvingautomated, programmable and/or robotic pipettors, and in processesemploying a plurality of tip columns, e.g., multiplexed processes.

In a process where a syringe or a manual pipettor is used, e.g., thetraditional, manually-operated Gilson Pipetman®, head pressure istypically not a major issue because the user can compensate for any headpressures in real-time during operation of the pipettor. For example, intaking up desorption solution the user will visually monitor the uptakeof fluid, and will intuitively retract the plunger enough to overcomeany residual positive pressure and draw the desired amount of liquidthrough the bed. Any adjustment of the head pressure is so trivial thatthe user will likely not be conscious of it. But this is a consequenceof the user being able to visually monitor fluid uptake and to adjustmovement of the plunger accordingly.

However, when using a programmable pipettor, such as an automatedmulti-channel pipettor (for example, the ME-200 instrument, availablefrom PhyNexus, Inc., San Jose, Calif.), the head pressure can become acritical issue. Typically, the pipettor pumps gas into or out of thehead space by movement of a displacing piston within a displacementcylinder having a displacement chamber and having another end with anaperture in communication with the head space (see, e.g., U.S. Pat. No.Nos. 4,905,526, 5,187,990 and 6,254,832). The rate and extent of pistonmovement (i.e., the piston displacement) is controlled by amicroprocessor, which is programmed by the operator. The operator willprogram an amount of piston displacement that will alter the headpressure sufficiently to draw or expel a desired amount of liquidthrough the bed. The amount of piston displacement required will dependupon the amount of liquid to be passed through the bed, the resistanceto flow through the bed (e.g., backpressure, surface tension), and mustalso be enough to compensate for any residual head pressure presentprior to pump displacement.

For example, consider the case where the next step in a process is theuptake of a desorption solution, and there is a residual positive headpressure as the result of a previous step of expelling a wash solution.In order to take up desorption solution, the operator must program themicroprocessor to direct a piston displacement sufficient to neutralizethe residual head pressure and then to introduce a negative pressureinto the head space sufficient to overcome resistance to flow and todraw up the desired amount of desorption solution. The volume ofdesorption solution is often small, and accurate uptake of the correctamount is important in order to achieve the optimal recovery andconcentration of the final product. It is apparent that in order toprogram the correct piston displacement, it is imperative that theresidual head pressure be known and accounted for, and/or that the headpressure be adjusted. If the head pressure is not taken into account,the piston displacement will be incorrect, as will the amount of liquidtaken up. The larger the head pressure, or variations in head pressure,relative to the amount of liquid taken up the more of an issue itbecomes.

For example, in FIG. 16 the head pressures at time 3 and 7 represent thehead pressures capable of drawing liquid in through the bed and to expelliquid out through the bed, respectively. Note that the difference inhead pressure between times 3 and 7 is less than 10 inches of water;thus, a difference in head pressure of less than 10 is the differencebetween fluid uptake and expulsion. Now consider the fluctuation in headpressure between times 1 and 2; the head pressure varies by greater than10 inches of water. This is the changes in head pressure that can begenerated as the syringe head space decreases (increasing the headpressure) and bubbles of air are intermittently force through the bed(decreasing the head pressure). Depending upon at what point in time theplunger depression is stopped, the head pressure can vary between 15 and25 inches of water at the stopping point. This head pressure is theresidual head pressure that must be accounted for when beginning thefluid uptake step, i.e., by beginning to pull up the plunger at time 2.The extent to which the plunger must be pulled up, i.e., the volume towhich the syringe chamber must be increased to draw up the desiredamount of liquid depends upon the residual head pressure. For example,if the residual head pressure is 25 the change in syringe chamber volumerequired to achieve the necessary negative head pressure will besubstantially less than if the residual head pressure is 15. A change insyringe chamber volume that is sufficient to draw up, e.g., 20 uL ofliquid when the residual head pressure is 15 will in many cases beinsufficient to draw up the same amount of liquid (or possibly anyliquid) when the residual head pressure is 25. On the other hand, achange in syringe chamber volume that is sufficient to draw up 20 uL ofliquid when the residual head pressure in 25 might be excessive when theresidual head pressure is only 15. An excessive change in head pressurevolume can lead to drawing up too much liquid. Or if the liquid is beingdrawn from a container (e.g., an eppendorf tube) containing only the 20uL of liquid, the excessive change in syringe chamber volume will resultin drawing up air through the bed after the 20 uL has been drawn up.This can negatively impact the outcome of a purification procedure,since it can result in bubbles of air being drawn up through the bedthat can break through and cause liquid to be splattered in the headspace. This can result in droplets of liquid becoming stuck to the wallsof the through passageway, instead of forming a continuous body ofliquid on top of the upper membrane. When the liquid is subsequentlypumped out of the bed, these droplets might be left behind. When theliquid is a small volume of desorption solution being used in a sampleelution step, these non-recovered droplets can result in substantialsample loss, i.e., low sample recovery.

Another scenario where residual head volume can pose substantialproblems in an automated purification process is where multiple pipettetip columns (two or more) are being used, either simultaneously or inseries. For example, consider an extraction process developed for usewith a particular pipette tip column, and intended to be used to extractsamples with multiple pipette tip columns of the same type, e.g.,substantially the same column dimensions, head space, extraction media,bed size, etc. As described above, the process will be accompanied byvariations in the head pressure, and particularly with the build up ofresidual head pressures (either negative or positive) that will bepresent prior to beginning each liquid uptake or expulsion step. Inpractice, what is often observed is that residual head pressure presentat any given step in the process will vary from column to column unlessmeasures are taken to adjust the head pressure. This variation can bethe result of any of a number of factors, including the type of headpressure fluctuations seen between times 1 and 2 in FIG. 16, and alsobecause of slight variations from column to column, reflecting subtledifference in the packing of the bed and of the interaction of the bedwith the frits and with the liquid, i.e., differential surfaced tensionand back pressure effects. Because the residual head pressures can varyfrom run to run and column to column, the appropriate extent of syringeplunger movement (equivalent to movement of the displacing piston in apipettor) will likewise vary.

This can be the case where multiple columns are run sequentially (inseries), and one wishes to program an automated pipettor to draw thecorrect amount of liquid at each step. If the residual head pressure atthe beginning of a given steps varies from column to column, then theappropriate displacement volume to achieve the desired amount of sampleuptake (or expulsion) will likewise vary.

This can also be the case when multiple columns are run concurrentlyand/or in parallel, e.g., as accomplished via a multi-channel pipettoror robotic liquid handling system. Because of subtle differences fromtip to tip, different residual head pressures can develop from tip totip. If these head pressures are not adjusted prior to a given step, andthe same pre-programmed volume displacement is used for each channel ofthe multi-channel device, then the types of problems discussed above canarise.

In certain embodiments, the invention provides methods of addressing theproblems associated with the above-described variations in headpressure. These methods involve adjusting the head pressure at varioussteps prior to and/or during a sample purification procedure.

In one approach to keeping the head pressure constant across several tipcolumns is to start with approximately the same liquid volume in eachtip and then avoid expelling or drawing air through any bed during thevarious steps in a purification process.

For example, the invention provides a method for passing liquid througha packed-bed pipette tip column comprising the steps of:

(a) providing a first column comprising: a column body having an openupper end for communication with a pump, a first open lower end for theuptake and dispensing of fluid, and an open passageway between the upperand lower ends of the column body; a bottom frit attached to andextending across the open passageway; a top frit attached to andextending across the open passageway between the bottom frit and theopen upper end of the column body, wherein the top frit, bottom frit,and surface of the passageway define a media chamber; a first packed bedof media positioned inside the media chamber; a first head space definedas the section of the open passageway between the open upper end and thetop frit, wherein the head space comprises a gas (typically air) havinga first head pressure; and a pump (e.g., a pipettor or syringe)sealingly attached to the open upper end, where actuation of the pumpaffects the first head pressure, thereby causing fluid to be drawn intoor expelled from the bed of media;

(b) contacting said first open lower end with a first liquid;

(c) actuating the pump to draw the first liquid into the first openlower end and through the first packed bed of media; and

(d) actuating the pump to expel at least some of the first liquidthrough the first packed bed of media and out of the first open lowerend.

In some embodiments, the method further comprising the following stepssubsequent to step (d):

e) contacting said first open lower end with a second liquid, which isoptionally the same as the first liquid;

f) actuating the pump to draw second liquid into the first open lowerend and through the first packed bed of media; and

g) actuating the pump to expel at least some of the second liquidthrough the first packed bed of media and out of the first open lowerend.

In various embodiments of the invention, the head pressure of the firstcolumn is adjusted at one or more points in the process, e.g., toaddress the head pressure issues discussed above. For example, the firsthead pressure of the first column can be adjusted between steps (d) and(f) to render the head pressure closer to a reference pressure, or equalor substantially equal to a reference head pressure. The reference headpressure can be any pressure desired to achieve the desired uptake orexpulsion of liquid when the pump is actuated. The pressure can bepredetermined, e.g., by determining the head pressure in a reference runwherein the degree of movement of a piston is calibrated to achieve theexpulsion or uptake of a desired amount of liquid. For example, thereference head pressure can be the head pressure of the first columnprior to step (c). The reference head pressure can be based upon astandard external to the head space, e.g., the ambient air pressure. Forexample, one way of adjusting the head pressure to a predetermined valueis to expose the head space to the external environment (by allowing airto pass to or from the head space), thereby normalizing the head spacepressure to the ambient pressure. This can be accomplished, e.g., bybreaking the seal between the upper open end and the pump (for example,by taking a pipette tip column off a pipettor and then putting it backon, thereby dispelling any negative or positive head pressure andnormalizing the head pressure to the ambient air pressure). For example,consider multiple pipette tip columns, each attached to a pipettorchannel and each having a different head pressure as a result a previousliquid uptake or expulsion operation. One could briefly disengage eachtip column from the pipettor channel, allowing the head space toequilibrate with the ambient air pressure and thereby normalizing thehead pressures. The same technique also applies to a single pipette tipcolumn; the normalization of the head pressure will assure consistenthead pressures at the beginning of a given step and equal volumes ofliquid taken up from run to run.

Some embodiments involve additional steps of:

(h) providing a second column comprising: a column body having an openupper end for communication with a pump, a second open lower end for theuptake and dispensing of fluid, and an open passageway between the upperand lower ends of the column body; a bottom frit attached to andextending across the open passageway; a top frit attached to andextending across the open passageway between the bottom frit and theopen upper end of the column body, wherein the top frit, bottom frit,and surface of the passageway define a media chamber; a second packedbed of media positioned inside the media chamber; a second head spacedefined as the section of the open passageway between the open upper endand the top frit, wherein the head space comprises a gas having a secondhead pressure; and a pump sealingly attached to the second open upperend, where actuation of the pump affects the second head pressure,thereby causing fluid to be drawn into or expelled from the secondpacked bed of media;

i) contacting said second open lower end with a third liquid, which isoptionally the same as the first liquid;

j) actuating the pump to draw the third liquid into the second openlower end and through the second packed bed of media;

k) actuating the pump to expel at least some of the third liquid throughthe second packed bed of media and out of the second open lower end.

l) contacting said second open lower end with a fourth liquid, which isoptionally the same as the third liquid;

m) actuating the pump to draw fourth liquid into the second open lowerend and through the second packed bed of media; and

n) actuating the pump to expel at least some of the fourth liquidthrough the second packed bed of media and out of the second open lowerend, wherein the head pressure of the second column is adjusted betweensteps (k) and (m) to render the head pressure closer to a referencepressure.

In some embodiments, steps (b) through (g) are performed prior to steps(i) through (n). In other embodiments steps (b) through (g) areperformed concurrently and in parallel with steps (i) through (n). Thatis the, two columns can be run sequentially or in parallel, such as inmultiplexed extraction procedures. In some embodiments, the referencehead pressure is the head pressure of the first column immediately priorto the commencement of step (f).

The pump can be any of the pumps described throughout thisspecification, such as a syringe pump or pipettor. For example, in someembodiments the pump is a multi-channel pipettor and the first column isattached to a first channel of the multi-channel pipettor and the secondcolumn is attached to a second channel of the multi-channel pipettor.

In some embodiments, between steps (d) and (f) the first head pressureis adjusted to render the first and second head pressures more uniform.In other methods the head pressures are adjusted to be more uniform atany other step in the process, particularly before any step involvingthe uptake or expulsion of liquid.

In some embodiments, the method is applied concurrently and in parallelto multiple pipette tip columns sealingly attached to a multi-channelpipettor (such as robotic workstation), wherein each pipette tip columncomprises a head space having a head pressure, and wherein the headpressures of the multiple pipette tip columns are adjusted to render thehead pressures more uniform. The multiple pipette tip columns cancomprise at least 2, at least 4, at least 6, at least 8, at least 16, atleast 32, at least 96, or more pipette tip columns. In some embodimentsthe head pressures of the multiple pipette tip columns are adjusted torender the head pressures substantially equal.

Head pressure can be adjusted by any of a number of methods. Asdescribed above, the head pressure can be adjusted by breaking thesealing attachment between the pump and the open upper end of a column,exposing the head space to ambient pressure, and sealingly reattachingthe pump to the open upper end of the column.

Alternatively, a column can be employed that includes a valve incommunication with the head space, and the head pressure is adjusted byopening this valve, thereby causing gas to enter or exit the head space.For example, a 3-way valve can be attached between a pump fitting and apipette tip column. Opening the valve will allow external air to enteror leave the head space, thereby allowing equilibration of the headpressure with the external pressure, e.g., the ambient pressure.

In another alternative, the head pressure is adjusted by means of thepump itself. The pump can be actuated to pump air into or out of thehead space, thereby adjusting the pressure of the head space to adesired level. In some embodiments a pressure sensor is positioned inoperative communication with a head space and used to monitor the headpressure and to determine the amount of gas to be pumped into or fromthe head space to achieve the desired pressure adjustment. The pressuresensor can provide real-time feedback to an automated pumping system(e.g., a multi-channel pipettor or robot) during a purification process,and cause the appropriate actuation of the pump to adjust the head spaceto a desired pressure. For example, in one embodiment a first columncomprises a first pressure sensor in operative communication with thefirst head space, a second pressure sensor in operative communicationwith the second head space, which is optionally the same as the firstpressure sensor, wherein said pressure sensors are used to monitor thefirst and second head pressures and to determine the amount of gaspumped into or from the second head space. The method can be applied toany number of multiple columns being used in parallel and/orsequentially.

In another embodiment, head pressure is adjusted by removing bulk liquidfrom the interstitial space of a packed bed of media, e.g., by blowingair through the bed. In some cases it takes relatively high headpressure to blow the residual liquid out of the bed, e.g., by rapidlypumping air through the bed. Often times, once the liquid has been blownout and replaced by air, air from outside the column can more easilytraverse the bed and enter the head space, thereby equilibrating thehead pressure with the ambient air pressure. This is because theresistance to air flow of a “dried bed” of extraction media is typicallysubstantially less than the resistance of the corresponding “wet bed.”The term “dried bed” refers to a bed wherein the interstitial space issubstantially void of liquid, although there can be some residual bulkliquid and the media itself might be hydrated. “Wet bed” refers to a bedwherein the interstitial space is substantially filled with liquid.Surface tension in the wet bed presumably restricts the flow of gasthrough the bed, allowing for maintenance of substantial pressuredifferentials between the head space and the external ambientenvironment.

In order to expel all liquid from a pipette tip column, the syringeplunger or displacing piston must be able to displace enough chambervolume to achieve the required positive head pressure. Consider the casewhere a displacing piston starts at a given starting positioncorresponding to a starting chamber volume. The piston is retracted,increasing the chamber volume and resulting in the uptake of liquid. Thepiston is then extended back to the starting position, reducing thechamber volume to the starting chamber volume. In some cases, due forexample to the surface tension and other effects described herein, theextension of the piston back to the starting position is insufficient toexpel all of the liquid from the tip as desired. It is thus necessary toextend the piston beyond the starting position to expel the full amountof liquid. This is impossible if the starting position of the piston isat the fully extended position, i.e., the typical starting point, wherethe chamber volume is at its minimum. Thus, in some embodiments ofinvention, the piston (or its equivalent, such as the plunger in asyringe) is retracted to some extent from the fully extended positionbefore beginning to take up any liquid, i.e., the starting position isdisplaced from the fully extended position, and hence the chamber volumeis greater than the minimum. This is advantageous in that it allows thepiston to be extended beyond the starting point during liquid expulsion,allowing for the creation of greater positive head pressure to expel allof the liquid from the column as desired. The greater the displacementof the starting position from the fully extended position, the greaterthe head pressure that can be created at the end of the extension step.The degree of displacement should be enough to compensate forbackpressures encountered in the particular column system at hand, andcan be determined empirically or calculated based on the properties ofthe column, sample liquid, pump system, etc.

Thus, in one embodiment the invention provides a method of purifying ananalyte comprising the steps of: (a) providing a column comprising: acolumn body having an open upper end for communication with a pump, anopen lower end for the uptake and dispensing of fluid, and an openpassageway between the upper and lower ends of the column body; a bottomfrit attached to and extending across the open passageway; a top fritattached to and extending across the open passageway between the bottomfrit and the open upper end of the column body, wherein the top frit,bottom frit, and surface of the passageway define a media chamber; apacked bed of media positioned inside the media chamber; a head spacedefined as the section of the open passageway between the open upper endand the top frit, wherein the head space comprises a gas having a headpressure; and a pump (e.g., a pipettor or syringe) sealingly attached tothe open upper end, wherein the pump includes a linear actuator (whichcan be controlled by an electrically driven microprocessor) and,connected to and controlled by the linear actuator, a displacementassembly including a displacing piston moveable within one end of adisplacement cylinder having a displacement chamber and having an endwith an aperture in communication with the head space; (b) positioningthe piston at a starting position that is displaced from a full-extendedposition that corresponds to a minimum displacement chamber volume,wherein the starting position is sufficiently displaced from thefully-extended position such that full extension of the piston willcause full expulsion of liquid from the column during an expulsion stepin the process (full expulsion being defined as the expulsion of allliquid or some of the liquid to the extent desired by the operator ofthe method); (c) positioning the open lower end into a liquid (eitherbefore, after, or concurrently with step (b)); retracting the piston todraw liquid through the open lower end and into the packed bed of media;and (d) extending the piston beyond the starting point, therebyexpelling the liquid through the packed bed of media and out of the openlower end.

Note that the above described method can result in a negative headpressure prior to retracting the piston and drawing up the liquid.

As discussed above, unintended variability in head pressure is often theresult of the intermittent seal formed by the bed of extraction mediaand media chamber. When the interstitial space is substantially full ofliquid, a seal is formed that prevents air from entering or leaving thehead space. If air is permitted to enter the bed during an extractionprocess it can form air channels in the bed through which air can pass,i.e., the seal is disrupted. Thus, in one embodiment of the inventionunintended variations in head pressure are prevented by maintaining theseal throughout an extraction process, e.g., by preventing air fromentering the chamber.

For example, in one embodiment, each actuation of the pump to drawliquid into the chamber comprises inducing a negative head pressure thatis sufficient to draw up a desired quantity of liquid but which is notso great as to cause air to enter the media chamber through the bottomfrit. In some embodiments, the induced negative pressure ispredetermined to be sufficient to draw up a desired quantity of liquidbut is not so great as to cause air to enter the media chamber throughthe bottom fit.

Methods that involve preventing entry of air into the media chamber areparticularly relevant in embodiments of the invention employing membranefrits.

In certain embodiments, after the liquid has been drawn into the mediachamber the outer surface of the bottom frit is in contact with air(e.g., all of the liquid in a well has been drawn up), but the air isprevented from entering or traversing the media chamber by a surfacetension that resists the passage of gas through the membrane frit andmedia chamber. Optionally, the magnitude of the negative pressure ispredetermined to be sufficient draw the liquid into the media chamberbut not so great as to overcome the surface tension that resists thepassage of gas through the membrane frit and media chamber. In somecases, there is a surface tension that resists the initial entry of theliquid through the open lower end of the column body and into the mediachamber, and the magnitude of the negative pressure is predetermined tobe sufficient to overcome the surface tension that resists the initialentry of the liquid through the open lower end of the column body andinto the media chamber.

One point at which there is a particular danger of air channels formingin the bed of extraction media is upon attachment of a column to a pump,e.g., attachment of a pipette tip column to a pipettor. Attachment ofthe tip will generally cause an increase in head pressure, and thisincrease in head pressure can drive liquid out of the interstitial spaceof the media bed and result in the formation of channels. A way to avoidthis is to ensure that there is sufficient liquid in the interstitialspace prior to attaching the tip to a pump, so that the interstitialspace remains substantially full of liquid. In this regard, it can beadvantageous to use a liquid that is more viscous than water as astorage liquid for a column, e.g., glycerol. A variety of water misciblesolvents, including glycerol, are described herein in connection withstorage of tips in a wet state. Thus, another advantage of many of thesesolvents is that they will be retained in the bed better than water, andwill be less likely to be forced out by head pressure resulting fromattachment of the column to a pump.

Maintaining Pipette Tip Columns and Polymer Beads in a Wet State

In certain embodiments, the invention provides methods of storingpipette tip columns in a wet state, i.e., with a “wet bed” of extractionmedia. This is useful in it allows for preparing the columns and thenstoring for extended periods prior to actual usage without the beddrying out, particularly where the extraction media is based on a resin,such as a gel resin. For example, it allows for the preparation of wetcolumns that can be packaged and shipped to the end user, and it allowsthe end user to store the columns for a period of time before usage. Inmany cases, if the bed were allowed to dry out it would adversely affectcolumn function, or would require a time-consuming extra step ofre-hydrating the column prior to use.

The maintenance of a wet state can be particularly critical wherein thebed volume of the packed bed is small, e.g, in a range having a lowerlimit of 0.1 μL, 1 μL, 5 μL, 10 μL, or 20μL, and an upper limit of 5 μL,10 μL, 20 μL, 50 μL, 100 μL, 200 μL, 300 μL, 500 μL, 1 mL, 2 mL, 5 mL,10 mL, 20 mL, or 50 mL. Typical ranges would include 0.1 to 100 μL, 1 to100 μL, 5 to μL, 10 to 100 μL, 1 to 20 μL, 1 to 10 μL, 5 to 20 μL, and 5to 10 μL.

The wet tip results from producing a tip having a packed bed of mediawherein a substantial amount of the interstitial space is occupied by aliquid. Substantial wetting would include beds wherein at least 25% ofthe interstitial space is occupied by liquid, and preferably at least50%, 70%, 80%, 90%, 95%, 98%, 99%, or substantially the entireinterstitial space is occupied by liquid. The liquid can be any liquidthat is compatible with the media, i.e., it should not degrade orotherwise harm the media or adversely impact the packing. Preferably, itis compatible with purification and/or extraction processes intended tobe implemented with the column. For example, trace amounts of the liquidor components of the liquid should not interfere with solid phaseextraction chemistry if the column is intended for use in a solid phaseextraction. Examples of suitable liquids include water, various aqueoussolutions and buffers, and various polar and non-polar solventsdescribed herein. The liquid might be present at the time the column ispacked, e.g., a solvent in which the extraction media is made into aslurry, or it can be introduced into the bed subsequent to packing ofthe bed.

In certain preferred embodiments, the liquid is a solvent that is watermiscible and that is relatively non-volatile and/or has a relativelyhigh boiling point (and preferably has a relatively high viscosityrelative to water). A “relatively high boiling point” is generally aboiling point greater than 100° C., and in some embodiments of theinvention is a boiling point at room temperature in range having a lowerlimit of 100° C., 110° C., 120° C., 130° C., 140° C., 150° C., 160° C.,170° C., 180° C., 190° C., 200° C., or higher, and an upper limit of150° C., 160° C., 170° C., 180° C., 190° C., 200° C., 220° C., 250° C.,300° C., or even higher. Illustrative examples would include alcoholhydrocarbons with a boiling point greater than 100° C., such as diols,triols, and polyethylene glycols (PEGs) of n=2 to n=150 (PEG-2 toPEG-150), PEG-2 to PEG-20, 1,3-butanediol and other glycols,particularly glycerol and ethylene glycol. The water miscible solventtypically constitutes a substantial component of the total liquid in thecolumn, wherein “a substantial component” refers to at least 5%, andpreferably at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%,98%, 99%, or substantially the entire extent of the liquid in thecolumn.

An advantage of these non-volatile solvents is that they are much lessprone to evaporate than the typical aqueous solutions and solvents usedin extraction processes. Thus, they will maintain the bed in a wet statefor much longer than more volatile solvents. For example, aninterstitial space filled with glycerol will in many cases stay wet fordays without taking any additional measures to maintain wetness, whilethe same space filled with water would soon dry out. These solvents areparticularly suitable for shipping and storage of gel type resin columnshaving agarose or sepharose beds. Other advantageous properties of manyof these solvents, is that they are viscous so it is not easilydisplaced from column from shipping vibrations and movements, they arebacterial resistant, they do not appreciably penetrate or solvateagarose, sepharaose, and other types of packing materials, and theystabilize proteins. Glycerol in particular is a solvent displaying thesecharacteristics. Note that any of these solvents can be used neat or incombination with water or another solvent, e.g., pure glycerol can beused, or a mixture of glycerol and water or buffer, such as 50% glycerolor 75% glycerol.

One advantage of glycerol is that its presence in small quantities hasnegligible effects on many solid-phase extraction process. A tip columncan be stored in glycerol to prevent drying, and then used in anextraction process without the need for an extra step of expelling theglycerol. Instead, a sample solution (typically a volume much greaterthan the bed volume, and hence much greater than the volume of glycerol)is loaded directly on the column by drawing it up through the bed andinto the head space as described elsewhere herein. The glycerol isdiluted by the large excess of sample solution, and then expelled fromthe column along with other unwanted contaminants during the loading andwash steps.

Note that relatively viscous, non-volatile solvents of the typedescribed above, particularly glyercol and the like, are generallyuseful for storing polymer beads, especially the resin beads asdescribed herein, e.g., agarose and sepharose beads and the like. Otherexamples of suitable beads would include xMAP® technology-basedmicrospheres (Luminex, Inc., Austin, Tex.). Storage of polymer beads asa suspension in a solution comprising one or more of these solvents canbe advantageous for a number of reasons, such as preventing the beadsfrom drying out, reducing the tendency of the beads to aggregate, andinhibiting microbial growth. The solution can be neat solvent, e.g.,100% glycerol, or a mixture, such as an aqueous solution comprising somepercentage of glycerol. The solution can also maintain the functionalityof the resin bead by maintaining proper hydration, and protecting anyaffinity binding groups attached to the bead, particularly relativelyfragile functional groups, such as certain biomolecules, e.g., proteins.

This method of storing suspensions of polymer beads is particularlyvaluable for storing small volume suspensions, e.g, volumes falling withranges having lower limits of 0.1 μL, 0.5 μL, 1 μL, 5 μL, 10 μL, 20 μL,50 μL, 100 μL, 250 μL, 500 μL, or 1000 μL, and upper limits of 1 μL, 5μL, 10 μL, 20 μL, 50 μL, 100 μL, 250 μL, 500 μL, 1 mL, 5 mL 10 mL, 20mL, or 50 mL. Typical, exemplary ranges would include 0.1 to 100 μL, 0.5to 100 μL, 1 to 100 μL, 5 to 100 μL, 0.1 to 50 μL, 0.5 to 50 μL, 1 to 50μL, 5 to 50μL, 0.1 to 20 μL, 0.5 to 20 μL, 1 to 20 μL, 5 to 20 μL, 0.1to 10 μL, 0.5 to 10 μL, 1 to 10 μL. 0.1 to 5 μL, 0.5 to 5 μL, 1 to 5 μL,and 0.1 to 1 μL.

Factors that can affect the rate at which a column dries include theambient temperature, the air pressure, and the humidity. Normallycolumns are stored and shipped at atmospheric pressure, so this isusually not a factor that can be adjusted. However, it is advisable tostore the columns at lower temperatures and higher humidity in order toslow the drying process. Typically the columns are stored under roomtemperature conditions. Room temperature is normally about 25° C., e.g.,between about 20° C. and 30° C. In some cases it is preferable to storethe pipette tip columns at a relatively low temperature, e.g., betweenabout 0° C. and 30° C., between 0° C. and 25° C., between 0° C. and 20°C., between 0° C. and 15° C., between 0° C. and 10° C., or between 0° C.and 4° C. In many cases tips of the invention may be stored at evenlower temperatures, particularly if the tip is packed with a liquidhaving a lower freezing point than water, e.g., glycerol.

In one embodiment, the invention provides a pipette tip column thatcomprises a bed of media, the interstitial space of which has beensubstantially full of liquid for at least 24 hours, for at least 48hours, for at least 5 days, for at least 30 days, for at least 60 days,for at least 90 days, for at least 6 months, or for at least one year.“Substantially full of liquid” refers to at least 25%, 50%, 70%, 80%,90%, 95%, 98%, 99%, or substantially the entire interstitial space beingoccupied by liquid, without any additional liquid being added to thecolumn over the entire period of time. For example, this would include acolumn that has been packaged and shipped and stored for a substantialamount of time after production.

In one embodiment, the invention provides a packaged pipette tip columnpackaged in a container the is substantially full of liquid, wherein thecontainer maintains the liquid in the pipette tip to the extent thatless than of 10% of the liquid is (or will be) lost when the tip isstored under these conditions for at least 24 hours, for at least 48hours, for at least 5 days, for at least 30 days, for at least 60 days,for at least 90 days, for at least 6 months, or for at least one year.

In another embodiment, the invention provides a pipette tip column thatcomprises a bed of media, the interstitial space of which issubstantially full of liquid, wherein the liquid is escaping (e.g., byevaporation or draining) at a rate such that less than 10% of the liquidwill be lost when the column is stored at room temperature for 24 hours,48 hours, 5 days, 30 days, 60 days, 90 days, six months or even oneyear.

In many cases, the wet pipette tip columns described above (e.g., thecolumn that has been wet for an extended period of time and/or thecolumn that is losing liquid only at a very slow rate) is packaged,e.g., in a pipette tip rack. The rack is a convenient means fordispensing the pipette tip columns, and for shipping and storing them aswell. Any of a variety of formats can be used; racks holding 96 tips arecommon and can be used in conjunction with multi-well plates,multi-channel pipettors, and robotic liquid handling systems.

In various embodiments, the invention provides methods for maintainingthe wetness of pipette tip columns. One method is illustrated in FIG.23. The pipette tip column 340 has a packed bed of media 346 positionedbetween upper frit 342 and lower frit 344. The packed bed is wet, i.e.,the interstitial space is substantially occupied by solvent, in thiscase an aqueous buffer. In order to inhibit drying of the bed, aquantity of the same aqueous buffer 350 (referred to as a storageliquid) is positioned in the head space 348. The tip is stored with thelower frit down, so gravity maintains the quantity of buffer at thelower end of the head space and in contact with the upper frit.Typically a small quantity of buffer in the head space will have littletendency to flow through the bed and out of the column due to theresistance to flow generated by the bed. The buffer in contact with thetop frit serves to maintain the wetness of the bed and frits.

In some embodiments, the pipette tip column is capped at the lower end344 and/or the upper end 352. This capping serves to restrictevaporation (i.e., desiccation) of liquid from the bed and to thusmaintain column wetness. The cap can be any solid substrate that coversthe end and fully or partially seals. Examples would be caps formed tofit the end, such as plastic or rubber caps. The cap could be a film orsheet, such as a film made of metal, plastic, polymeric material or thelike. A film or sheet is particularly suited to capping multiple caps.For example, a plurality of tips in a tip rack can all be capped attheir upper ends with a sheet of foil or plastic film that is laid overand in contact with the tip tops. The cap can be attached to the openingby pressure, or by some adhesive, or any means that will result in afull or partial seal sufficient to inhibit evaporation of liquid fromcolumn. For example, a single sheet of foil or plastic can be glued tothe top of a plurality of tips arranged in a rack. Preferably theadhesive is one that can does not bind too tightly (i.e., the cap isremovably adhered to the column), so that the tips can be uncapped priorto use, and such that the adhesive does not leave a residue on the tipthat would interfere with an extraction process. Alternatively, a sheetcan be held in contact with the upper ends of the tips by pressure. Forexample, a sealing sheet can be draped over the upper ends of tips in arack and a hard cover placed on top of that and in contact with thesheet, thus pressing the sheet against the tops of the tips to form afull or partial seal.

End capping is particularly effective when used in combination withstorage liquid in the head space, as described above. The capping of oneor both ends restricts the loss of storage liquid, and the storageliquid maintains the wetness of the bed for extended periods of time.

Another method of maintaining column wetness is by packing the tipcolumn in the presence of an antidessicant. An “antidessicant” is anymaterial that is able to moisturize or humidify an environment. Oneuseful antidessicant is hydrated polyacrylamide. For example, anenclosed pipette tip container (a tip rack) can be used for tip storage,wherein the antidessicant is placed in the container and provides amoist environment that resists dessication of tip columns in thecontainer. In some embodiments, the cap itself comprises anantidessicant. For example, in one preferred embodiment, a porous bagcontaining hydrated polyacrylamide is used as the cap. The bag caps thetip columns by being pressed against the open upper or lower ends of thetips. Thus, the bag not only inhibits loss of liquid from the column bysealing off the head space and/or bed from the external environment, italso provide a very moist environment.

Positioning Tips for Use in Multiplexed Processes

In some embodiments methods of the invention involve multiplexedextraction by means of a plurality of pipette tip columns and amulti-channel pipettor. The methods can involve drawing liquid from awell in a multi-well plate. The volume of liquid can be relativelysmall, e.g., on the order of 10 μL or less of desorption solution, andit is often important that substantially the entire volume of liquid istaken up by each of the tips. To achieve this, it is critical that theopen lower end of each pipette tip column is accurately placed at aposition in each well that is in contact with the fluid and submerged ata depth such that substantially all of the liquid will be drawn into thetip upon application of sufficient negative pressure in the head space.Typically this position is near the center of a circular well, at adepth that is near the bottom of the well (within one to severalmillimeters) but preferably not in direct contact with the bottom. Ifthe tip makes direct contact with the well surface there is the dangerthat a seal might form between tip and well that will restrict flow ofliquid into and/or out of the tip. However, contact between the tip andwell bottom will not necessarily prevent or restrict flow into the tip,particularly if no seal is formed between the tip and well.

A problem that can arise in a multiplexed purification process is thatit can be difficult to accurately position all of the tips on amultichannel pipettor such that each is at the optimal position in itscorresponding well. For example, if the open lower ends of each tip arenot positioned in substantially a straight line (for a linearconfiguration of tips) or a plane (for at two-dimensional array oftips), and that line (or plane) is not substantially parallel to thebottoms of the corresponding array of wells in a plate, then it will bevery difficult to simultaneously position each tip at its optimallocation. This is illustrated in FIG. 24, which depicts eight pipettetip columns 360 attached to an eight channel pipettor 362. The tips arepositioned in the wells of a multi-well plate 364, over and close to thebottom of the wells. Because the pipettor is at a slight angle inrelation to the plate, the tip at the far right 366 is making contactwith the bottom of the well 368, which can restrict flow of liquidthrough the tip. On the other hand, the tip to the far left 370 ispositioned too high, and will not be able to fully draw up a smallaliquot of liquid from the bottom of the well 372.

Thus, in one embodiment the invention provides a method for accuratelypositioning a plurality of tip columns into the wells of a microwellplate. The method as applied to a linear configuration of pipette tipcolumns is exemplified in FIG. 25. In this case, positioning tips 380that extend slightly longer than the pipette columns are positioned ateither end of the row of pipette tip columns, in an arrangementreminiscent of “vampire teeth.” In operation, the positioning tips arepositioned so that both rest against the bottom of their correspondingwells 382. The pipette tip columns internal to the two positioning tipsare elevated from the bottom of their wells be a distance equal to thedistance the positioning tips extend beyond the ends of the pipettetips. Thus, by adjusting the length of the positioning tips it ispossible to position the internal tips 384 at any desired distance fromthe bottom of their corresponding wells. The positioning tips greatlysimplify and stabilize the positioning of the pipette tips at apredetermined and uniform distance from the well bottoms.

Note that as depicted in FIG. 25, there are two positioning tips, one ateither end of the row of tips. In alternative embodiments a singlepositioning tip could be used, e.g., at a position near the center ofthe row like tip 386. In general, the use of a single positioning tipwill not afford the stability and accuracy of a multi-positioning tipformat, but it will be better than not using a positioning tip at alland in some instances will be sufficient.

Alternatively, more than two positioning tips could be used, althoughnormally two is sufficient for a linear arrangement of pipette tips.However, if the row of tips is significantly longer than eight tips inlength, then it might be the case that the additional stability providedby more than two positioning tips is beneficial.

Note that whether one or more tips are used, it is not necessary thatthe positioning tips take any particular position relative to the tipcolumns. For example, the arrangement of FIG. 25 could be varied suchthat the positioning tips are positioned at positions 388, and positions380 might in this scenario be occupied by functional tip columns.

The positioning tips will make contact with a reference point that islocated at a fixed, predetermined location relative to the well bottomscorresponding to pipette tip columns. For example, the reference pointcan be a well bottom not being used in an extraction process. Forexample, FIG. 27 depicts a 96 well plate. The four corner wells 390 arenot used to hold liquid but are rather used as reference points;positioning tips located at the four corners of the two-dimensionalarray of pipette tip columns in FIG. 26 are brought into contact withthe bottoms of the wells 390 to correctly position the pipette tipcolumns in the corresponding wells of the plate.

The method is also suitable for use with a two-dimensional array oftips, such as on a multi-channel pipettor having more than one row oftip columns, e.g., a 96 channel pipettor that is part of a robotic fluidhandling system. For example, FIG. 26 depicts an 8×12 array of 96pipette tip columns and positioning tips. In this particular example,the positioning tips are at the corners of the array 392. As was thecase with linear configurations of tips, in two-dimensional arrays thereare a variety of alternative options for the number and location of thepositioning tips. For example, in a preferred embodiment fourpositioning tips are used, one at each corner of the array of tips.Alternatively, more or less than four positioning tips could be used,e.g., two tips, one at each of two opposite corners, or a single tiplocated at a corner or internal position in the array.

Thus, in certain embodiments the invention provides a general method ofpositioning a pipette tip column in relative to a well bottom comprisingthe steps of: (a) providing a pipetting system comprising: (i) apipettor; (ii) a pipette tip column having an open upper end operativelyengaged with said pipettor and an open lower end for passing solutionthrough the pipette tip column; and (iii) a positioning tip attached tosaid pipettor, said positioning tip having a proximal end attached tothe pipettor and a distal end positioned at a fixed., predeterminedlocation relative to the open lower end of the pipette tip column; and(b) positioning the pipetting system so that: (i)the distal end of thepositioning tip makes contact with a reference point, wherein saidreference point is located at a fixed, predetermined location relativeto a well having a well bottom; and (ii) the open lower end of thepipette tip column is positioned over the well bottom.

The pipetting system can be part of a robotic liquid handling system.

In certain embodiments the well contains a liquid, e.g., a sample, washor desorption solution. In certain embodiments the pipetting system ispositioned so that the open lower end of the pipette tip column makescontact with the liquid, and the pipettor is activated to draw liquidthrough the open lower end and into the pipette tip column.

In certain embodiments the pipettor is a multi-channel pipettor.

Particularly in cases where the pipettor is a multi-channel pipettor,the pipetting system can comprise a plurality of pipette tip columns,each pipette tip column having an open upper end operatively engagedwith said pipettor and an open lower end for passing solution throughthe pipette tip column, wherein the pipetting system is positioned sothat: (i) the distal end of the positioning tip makes contact with areference point, wherein said reference point is located at a fixed,predetermined location relative to a well having a well bottom; and (ii)the open lower end of each of the pipette tip column is positioned overa well bottom of one of the plurality of wells.

In certain embodiments positioning tip is a pipette tip, a pipette tipcolumn, or some other object capable of attachment to the pipettor. Theattachment can be transient, or the positioning tip can be permanentlyaffixed to the pipettor or even an integral component of the pipettor.

In certain embodiments the wells are all elements of a multi-well plate.e.g., microwells.

In certain embodiments of the invention involving a multi-well plate,the reference point can be located on the multi-well plate, e.g., thereference point can be the bottom of a well of the multi-well plate.

In certain embodiments, a plurality of positioning tips is used, eachpositioning tip making contact with a reference point located at afixed, predetermined location relative to the plurality of wells.

In certain embodiments, the volume of liquid in the wells is relativelylow, e.g., in a range having a lower limit of 0.1 μL, 0.5 μL, 1 μL, 2μL, 5 μL or 10 μL, and an upper limit of 1 μL, 2 μL, 5 μL 10 μL, 20 μL,30 μL, 50 μL, 100 μL, 200 μL or even 500 μL. For example, in certainembodiments the volume of liquid in the wells is of between 1 and 100μL, or 1 and 20 μL, or 5 and 20 μL.

In certain embodiments, the open lower end of the pipette tip column ispositioned close enough to the well bottom such that upon activation ofthe pipettor substantially all of the liquid is drawn through the openlower end and into the pipette tip column, but not so close as to form aseal with the well bottom.

The open lower end of the pipette tip column is typically positionedrelatively close to the corresponding well bottom, e.g., within a rangehaving a lower limit of about 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 m,0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm from the bottom of the well, andan upper limit of 0.3 mm, 0.4 m, 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6mm, 7 mm, 8 mm, 8 mm or 10 mm of the well bottom. For example, in someembodiments the open lower end of a pipette tip column is positionedwith between 0.05 and 2 mm from a well bottom, or between 0.1 and 1 mmfrom a well bottom. The term “well bottom” does not necessarily refer tothe absolute bottom of a well, but to the point where the tip makescontact with the well when the tip is lowered to its full extent intothe well, i.e., a point where the tip can seal with the well surface.For example, in some microwell plate formats the wells taper down to aninverted conical shape, so a typical tip column will not be able to makecontact with the absolute bottom of the well.

In certain embodiments, the positioning tips are longer than the pipettetip columns. The difference in length between positioning tips andpipette tip columns can result in accurately locating the ends of thepipette tip columns at a desired distance from the bottoms of thecorresponding wells. The difference in length between positioning tipsand pipette tip columns can be relatively small, e.g. in a range havinga lower limit of 0.1 mm, 0.2 mm, 0.5 mm, 1 mm or 2 mm and an upper limitof 1 mm, 2 mm, 3 mm, 4 mm, 5 mm 6 mm, 7 mm, 8 mm, 8 mm or 10 mm. Forexample, in certain embodiments the positioning tips are between 1 and10 mm longer than the pipette tip columns.

In certain embodiments, a plurality of pipette tip columns andpositioning tips are attached to a multi-channel pipettor in a linearconfiguration. For example, the positioning tips can be positioned atthe two ends of the linear configuration of pipette tip columns andpositioning tips, e.g., see FIGS. 24 and 25.

In certain embodiments, a plurality of pipette tip columns andpositioning tips are attached to a multi-channel pipettor in atwo-dimensional array. The two-dimensional array can comprise fourcorners, with positioning tips are positioned at two or more of thecorners. For example, the positioning tips can be positioned at fourcorners of a two-dimensional array, e.g., see FIGS. 26 and 27.

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

Having now generally described the invention, the same will be morereadily understood through reference to the following examples, whichare provided by way of illustration, and are not intended to be limitingof the present invention, unless so specified.

EXAMPLES

The following preparations and examples are given to enable thoseskilled in the art to more clearly understand and practice the presentinvention. They should not be construed as limiting the scope of theinvention, but merely as being illustrative and representative thereof.

Example 1

Preparation of an Extraction Column Body from Pipette Tips

Two 1000 μL polypropylene pipette tips of the design shown in FIG. 6(VWR, Brisbane, Calif., PN 53508-987) were used to construct oneextraction column. In this example, two extraction columns wereconstructed: a 10 μL bed volume and 20 μL bed volume. To construct acolumn, various components were made by inserting the tips into severalcustom aluminum cutting tools and cutting the excess material extendingout of the tool with a razor blade to give specified column lengths anddiameters.

Referring to FIG. 7, the first cut 92 was made to the tip of a pipettetube 90 to form a 1.25 mm inside diameter hole 94 on the lower columnbody, and a second cut 96 was made to form a lower column body segment98 having a length of 15.0 mm.

Referring to FIG. 8, a cut 102 was made to the separate pipette tip 100to form the upper column body 104. To make a 10 μL bed volume column,the cut 102 was made to provide a tip 106 outside diameter of 2.09 mm sothat when the upper body was inserted into the lower body, the columnheight of the solid phase media bed 114 (FIG. 10) was 4.5 mm. To make a20 μL bed volume column, the cut 102 was made to provide a tip outsidediameter of 2.55 mm cut so that when the upper body was inserted intothe lower body, the column height of the solid phase media bed 114 (FIG.10) was 7.0 mm.

Referring to FIG. 9, a 43 μm pore size Spectra/Mesh® polyester meshmaterial (Spectrum Labs, Ranch Dominguez, Calif., PN 145837) was cutinto discs by a circular cutting tool (Pace Punches, Inc., Irvine,Calif.) and attached to the ends 106 and 108 of the upper column andlower column bodies to form the membrane screens 110 and 112. Themembrane screens were attached using PLASTIX® cyanoacrylate glue(Loctite, Inc., Avon, Ohio). The glue was applied to the polypropylenebody and then pressed onto the membrane screen material. Using a razorblade, excess mesh material was removed around the outside perimeter ofeach column body end.

Referring to FIG. 10, the upper column body 104 is inserted into the topof the lower column body segment 98 and pressed downward to compact thesolid phase media bed 114 to eliminate excess dead volume above the topof the bed.

Example 2

Preparation of SEPHAROSE™ Protein G and MEP HYPERCEL™ Extraction Columns

Referring to FIG. 9, a suspension of Protein G SEPHAROSE™ 4 Fast Flow,45-165 μm particle size, (Amersham Biosciences, Piscataway, N.J., PN17-0618-01) in water/ethanol was prepared, and an appropriate amount ofmaterial 114 was pipetted into the lower column body 98.

Referring to FIG. 10, the upper column body 104 was pushed into thelower column body 98 so that no dead space was left at the top of thebed 114, that is, at the top of the column bed. Care was taken so that aseal was formed between the upper and lower column bodies 104 and 98while retaining the integrity of the membrane screen bonding to thecolumn bodies.

Several tips of 10 μL and 20 μL bed volumes were prepared. Several MEP(Mercapto-Ethyl-Pyridine) HYPERCEL™ (Ciphergen, Fremont, Calif., PN12035-010) extraction columns were prepared using the same procedure.MEP HyperCel™ resin is a sorbent, 80-100 μm particle size, designed forthe capture and purification of monoclonal and polyclonal antibodies.The extraction columns were stored with an aqueous solution of 0.01%sodium azide in a refrigerator before use.

Example 3 Purification of Anti-leptin Monoclonal Antibody IgG with 10 μLand 20 μL Bed Volume Protein G SEPHAROSE™ Extraction Columns

A Protein G SEPHAROSE™ 4 Fast Flow (Amersham Biosciences, Piscataway,N.J., PN 17-0618-01) extraction column was prepared as described inExample 2.

Five hundred μL serum-free media (HTS Biosystems, Hopkinton, Mass.)containing IgG (HTS Biosystems, Hopkinton, Mass.) of interest wascombined with 500 μL standard PBS buffer. The resulting 1 mL sample waspulled into the pipette tip, through the Protein G packed bed at a flowrate of approximately 1 mL/min) or roughly 15 cm/min). The sample wasthen pushed out to waste at the same approximate flow rate. Extraneousbuffer was removed from the bed by pulling 1 mL of deionized water intothe pipette column at about 1 mL/min and pushing it out at about 1mL/min. The water was pushed out as much as possible to achieve as dryof a column bed as is possible. The IgG was eluted from the column bedby drawing up an appropriate eluent volume of 100 mM glycine.HCl, pH 2.5(20 μL eluent in the case of a 20 μL bed volume, 15 μL eluent in thecase of a 10 μL bed volume). When the eluent was fully drawn into thebed, it was “pumped” back and forth through the bed five or six times,and the IgG-containing eluent was then fully expelled from the bed. Theeluted material was then neutralized with 100 mM NaH₂PO₄/100 mM Na₂HPO₄(5 μL neutralization buffer in the case of a 20 μL bed volume, 4 μLneutralization buffer in the case of a 10 μL bed volume). The purifiedand enriched antibodies were then ready for arraying.

Example 4 Purification of Anti-leptin Monoclonal Antibody IgG with 10 μLand 20 μL Bed Volume Protein G SEPHAROSE™ Extraction Columns

A Protein G SEPHAROSE™ 4 Fast Flow (Amersham Biosciences, Piscataway,N.J., PN 17-0618-01) extraction column was prepared as described inExample 2.

Five hundred μL serum-free media (HTS Biosystems, Hopkinton, Mass.)containing IgG (HTS Biosystems, Hopkinton, Mass.) of interest wascombined with 500 μL standard PBS buffer. The resulting 1 mL sample waspulled into the pipette tip, through the Protein G packed bed at a flowrate of approximately 1 mL/min (or roughly 150 cm/min linear velocity).The sample was then pushed out to waste at the same approximate flowrate. Extraneous buffer was removed form the bed by pulling 1 mL ofdeionized water into the pipette column at about 1 mL/min and pushing itout at about 1 mL/min. The water was pushed out as much as possible toachieve as dry of a column bed as is possible. The IgG was eluted fromthe column bed by drawing up an appropriate eluent volume of 10 mMphosphoric acid (H₃PO₄), pH 2.5 (20 μL eluent in the case of a 20 μL bedvolume, 15 μL eluent in the case of a 10 μL bed volume). When the eluentwas fully drawn into the bed, it was “pumped” back and forth through thebed five or six times, and the IgG-containing eluent is then fullyexpelled from the bed. The eluted material was then neutralized with aspecially designed phosphate neutralizing buffer of 100 mM H₂NaPO₄/100mM HNa₂PO₄, pH 7.5 (5 μL neutralization buffer in the case of a 20 μLbed volume, 4 μL neutralization buffer in the case of a 10 μL bedvolume). The purified and enriched antibodies were then ready forarraying.

Example 5 Analysis of Purified IgG with Grating-coupled Surface PlasmonResonance (GC-SPR)

The anti-leptin monoclonal antibody IgG purified sample from Example 4was analyzed with GC-SPR. The system used for analysis was a FLEX CHIP™Kinetic Analysis System (HTS Biosystems, Hopkinton, Mass.), whichconsists of a plastic optical grating coated with a thin layer of goldon to which an array of biomolecules is immobilized. To immobilize thepurified IgG, the gold-coated grating was cleaned thoroughly with EtOH(10-20 seconds under a stream of ETOH). The gold-coated grating was thenimmersed in a 1 mM solution of 11-mercaptoundecanoic acid (MUA) in EtOHfor 1 hour to allow for the formation of a self-assembled monolayer. Thesurface was rinsed thoroughly with EtOH and ultra-pure water, and driedunder a stream of nitrogen. A fresh solution of 75 mM EDC(1-Ethyl-3-(3-Dimethylaminopropyl) carbodiimide hydrochloride) and 15 mMSulfo-NHS (N-Hydroxysulfo-succinimide) was prepared in water. An aliquotof the EDC/NHS solution was delivered to the surface and allowed toreact for 20-30 minutes, and the surface was then rinsed thoroughly withultra-pure water. An aliquot of 1 mg/mL Protein A/G in PBS, pH 7.4 wasdelivered to the surface. The surface was placed in a humid environmentand allowed to react for 1-2 hours. The surface was allowed to air dry,was rinsed with ultra-pure water and then dried under a stream ofnitrogen. Immediately prior to arraying of the IgGs, the surface wasrehydrated by placing in a humidified chamber, such as available withcommercial arraying systems (e.g. Cartesian MicroSys synQUAD System).The purified anti-leptin IgG was arrayed onto the surface as describedpreviously (J. Brockman, et al, “Grating-Coupled SPR: A Platform forRapid, Label-free, Array-Based Affinity Screening of Fabs and Mabs”,12^(th) Annual Antibody Engineering Conference, Dec. 2-6, 2001, SanDiego, Calif.) and the surface was introduced to the HTS Biosystems FLEXCHIP System. 150 nM leptin in PBS, pH 7.4 was introduced to the surfacethrough the FLEX CHIP System, and real-time binding signals werecollected as described previously (ibid.). These real-time bindingsignals were mathematically processed in a manner described previously(D. Myszka, “Kinetic analysis of macromolecular interactions usingsurface plasmon resonance biosensors”, Current Opinion in Biotechnology,1997, Vol 8, pp. 50-57) for extraction of the association rate (k_(a)),dissociation rate (k_(d)), and the dissociation affinity constant(K_(d)=k_(d)/k_(a)). The kinetic data obtained is shown in Table IIbelow.

TABLE II Serum-free medium PBS No processing Mean K_(d)   18 nM  3.2 nM(Adequate [IgG]) Starting [IgG]  500 μg/mL  500 μg/mL With processingMean K_(d)  6.6 nM  5.9 nM* (Insufficient [IgG] Starting [IgG]   20μg/mL  500 μg/mL* *500 μg/mL IgG in PBS was not processed, but wasincluded in the SPR analysis for the purpose of comparing dissociationaffinity constants calculated for each

The first set of data for “No processing” indicates that when sufficientIgG is present for detection (500 μg/mL) that the constituents from theserum-free medium can contribute to inaccuracies. These data indicatefor equal concentrations of IgG spotted within an experiment, thecalculated dissociation affinity constant can be nearly six-folddifferent from one another (18 nM vs 3.2 nM). This can only be a resultof components within the serum-free medium being co-arrayed with theIgG, since the concentration and composition of IgG is identical foreach sample. Therefore, there is a demonstrated need for removal of anyextraneous components prior to arraying, which is independent of IgGconcentration.

The second set of data for “With processing” indicates that wheninsufficient IgG quantities are present for detection (20 μg/mL) thatsample processing not only allows for generation of sufficientprocessable signals, but also eliminates the inaccuracies generated fromextraneous components. These data indicate that the dissociationaffinity constants are virtually identical for 500 μg/mL purified IgG inPBS (unprocessed) as those calculated from 20 μg/mL IgG in serum-freemedium once processed with the current invention (5.9 nM vs 6.6 nM).

Example 6 Purification of Nucleic Acids with an Extraction Column

Columns from Example 1 are bonded with a 21 μm pore size SPECTRA/MESH®polyester mesh material (Spectrum Labs, Ranch Dominguez, Calif., PN148244) by the same procedure as described in Example 2. A 10 μL bedvolume column is filled with PELLICULAR C18 (Alltech, Deerfield, Ill.,PN 28551), particle size 30-50 μm. One end of the extraction column isconnected to a pipettor pump (Gilson, Middleton, Wis., P-1000PipetteMan) and the other end is movable and is connected to anapparatus where the materials may be taken up or deposited at differentlocations.

The extraction column consists of a 1 mL syringe (VWR, Brisbane, Calif.,PN 53548-000), with one end connected to a pipettor pump (Gilson,Middleton, Wis., P-1000 PipetteMan) and the other end is movable and isconnected to an apparatus where the materials may be taken up ordeposited at different locations.

A 100 μL sample containing 0.01 μg of DNA is prepared using PCRamplification of a 110 bp sequence spanning the allelic MstII site inthe human hemoglobin gene according to the procedure described in U.S.Pat. No. 4,683,195. A 10 μL concentrate of triethylammonium acetate(TEAA) is added so that the final volume of the solution is 110 μL andthe concentration of the TEAA in the sample is 100 mM. The sample isintroduced into the column and the DNA/TEAA ion pair complex isadsorbed.

The sample is blown out of the column and 10 μL of 50% (v/v)acetonitrile/water is passed through the column, desorbing the DNA, andthe sample is deposited into a vial for analysis.

Example 7 Desalting Proteins with an Extraction Column

Columns from Example 1 are bonded with a 21 μm pore size SPECTRA/MESH®polyester mesh material (Spectrum Labs, Ranch Dominguez, Calif., PN148244) by the same procedure as described in Example 2. A 10 μL bedvolume column is filled with PELLICULAR C18 (Alltech, Deerfield, Ill.,PN 28551), particle size 30-50 μm. One end of the extraction column isconnected to a pipettor pump (Gilson, Middleton, Wis., P-1000PipetteMan) and the other end is movable and is connected to anapparatus where the materials may be taken up or deposited at differentlocations.

The sample is a 100 μL solution containing 0.1 μg of Protein kinase A ina phosphate buffer saline (0.9% w/v NaCl, 10 mM sodium phosphate, pH7.2) (PBS) buffer. Ten μL of 10% aqueous solution of trifluoroaceticacid (TFA) is added so that the final volume of the solution is 110 μLand the concentration of the TFA in the sample is 0.1%. The sample isintroduced into the column and the protein/TFA complex is adsorbed tothe reverse phase of the bed.

The sample is blown out of the column and 10 μL of 50% (v/v)acetonitrile/water is passed through the column, desorbing the proteinfrom the bed of extraction media, and the sample is deposited into avial for analysis.

Alternatively, the bed may be washed with 10 μL of aqueous 0.1% TFA.This solution is ejected from the column and the protein is desorbed anddeposited into the vile.

If necessary, alternatively 1% heptafluorobutyric acid (HFBA) is usedinstead of TFA to reduce ion suppression effect when the sample isanalyzed by electrospray ion trap mass spectrometry.

Example 8 Straight Connection Configuration

This example describes an embodiment wherein the column body isconstructed by engaging upper tubular members and membrane screens in astraight configuration.

Referring to FIG. 11, the column consists of an upper tubular member120, a lower tubular member 122, a top membrane screen 124, a bottommembrane screen 126, and a lower tubular circle 134 to hold the bottommembrane screen in place. The top membrane screen is held in place bythe upper and lower tubular members. The top membrane screen, bottommembrane screen and the channel surface 130 of the lower tubular memberdefine an extraction media chamber 128, which contains a bed ofextraction media (i.e., packing material). The tubular members asdepicted in FIG. 11 are frustoconical in shape, but in relatedembodiments could take other shapes, e.g, cyclindrical.

To construct a column, various components are made by forming injectedmolded members from polypropylene or machined members from PEEK polymerto give specified column lengths and diameters and ends that can fittogether, i.e., engage with one another. The configuration of the maleand female portions of the column body is shaped differently dependingon the method used to assemble the parts and the method used to keep theparts together.

The components are glued or welded. Alternatively, they are snappedtogether. In the case of snapping the pieces together, the femaleportion contains a lip and the male portion contains a ridge that willhold and seal the pieces once they are assembled. The membrane screen iseither cut automatically during the assembly process or is trimmed afterassembly.

Example 9 End Cap and Retainer Ring Configuration

This example describes an embodiment where an end cap and retainer ringconfiguration is used to retain the membrane screens containing a 20 μlbed of column packing material. The embodiment is depicted in FIG. 12.

Referring to the figure, pipette tip 140 (VWR, Brisbane, Calif., PN53508-987) was cut with a razor blade to have a flat and straight bottomend 142 with the smooth sides such that a press fit can be performedlater. An end cap 144 was machined from PEEK polymer tubing to containthe bottom membrane screen 146.

Two different diameter screens were cut from polyester mesh (SpectrumLabs, Ranch Dominguez, Calif., PN 145836) by a circular cutting tool(Pace Punches, Inc., Irving, Calif.), one for the top membrane screen148 and the other for the bottom membrane screen 146. The bottommembrane screen was placed into the end cap and pressed onto the end ofthe cut pipette tip.

A 20 μL volume bed of beads was formed by pipetting a 40 μL of 50%slurry of protein G agarose resin into the column body.

Two retainer rings were used to hold the membrane screen in place on topof the bed of beads. The retainer rings were prepared by taking ⅛ inchdiameter polypropylene tubing and cutting thin circles from the tubingwith a razor blade. A first retainer ring 152 was placed into the columnand pushed down to the top of the bed with a metal rod of similardiameter. The membrane screen 148 was placed on top of the firstretainer ring and then a second retainer ring 154 was pushed down to“sandwich” the membrane screen while at the same time pushing the wholescreen configuration to the top of the bed and ensuring that all deadvolume was removed. The two membranes define the top and bottom of theextraction media chamber 150, wherein the bed of beads is positioned.The membrane is flexible and naturally forms itself to the top of thebed.

The column was connected to a 1000 μL pipettor (Gilson, Middleton, Wis.,P-1000 PipetteMan) and water was pumped through the bed and dispensedfrom the bed. The column had low resistance to flow for water solvent.

Example 10 Production of a Micro-bed Extraction Column

To manufacture a 0.1 μL bed, a polyester membrane is welded onto one endof a polypropylene tube of 300 mm inside diameter and 4 mm long. The bedis filled with a gel resin material to a height of 0.25 mm. A smallcircle or wad of membrane frit material is pushed into the end of thecolumn. Then a 5 cm long fused silica capillary (320 μm od, 200 μm id)is inserted into the top of the polypropylene tube and pushed down tothe top of the column bed. A fitting is used to attach a micro-syringepump to the column, which allows for solution to be drawn in and out ofthe bed, for use in a micro-scale extraction of the type describedherein.

Columns with various small bed volumes can be constructed usingdifferent pipette tips as starting materials. For example, a 0.5 μL bedcolumn (0.4 mm average diameter and 0.4 mm length can be constructedusing 10 μL pipette tips (Finnitip 10 from Thermolab Systems, Cat. No.9400300). The membrane screen can be attached gluing, welding andmechanical attachment. The bed volume can be controlled more easily bygluing the membrane screen. Other columns with the sizes of 1.2, 2.2,3.2, and 5.0 μL beds were made in a similar way from P-235 pipette tipsavailable from Perkin Elmer (Cat. No. 69000067).

Example 11 Evaluation of a 10 μL Bed Volume Pipet Tip Column Containinga Protein A Resin

In this example, the performance of 10 μL bed volume pipet tip columns(manufactured from 1 mL pipet tips (VWR)) containing a Protein A resinwas evaluated. The resins under consideration consist of purifiedrecombinant protein A covalently coupled through multi-point attachmentvia reductive amidation to 6% highly cross-linked agarose beads(RepliGen Corporation, IPA400HC; PN: 10-2500-02) or to 4% cross-linkedsepharose beads (Amersham-Pharmacia). The samples tested consisted of 15μg mFITC-MAb (Fitzgerald, Inc. Cat # 10-F50, mouse IgG_(2a)) in 0.5 mlof PBS or PBS containing 5 mg BSA (10 mg/ml or 1% m/v BSA).

An ME-100 multiplexing extraction system (Phynexus, Inc.) was used, themajor elements of which are illustrated schematically in FIG. 13 and inthe text accompanying that figure. The system was programmed to blow outthe bulk of the storage solution from the tips prior to taking up thesamples. The 0.5 mL samples were provided in 1.5 ml eppendorf tubes andpositioned in the sample rack, which was raised so that the tip of thecolumns made contact with the sample. During the load cycle, 2 or 5in/out cycles were employed (depending upon the test), the volume drawnor ejected programmed at 0.6 ml @0.25 ml/min.

After loading, the extraction beds were washed with 2 in/out cycles,volume programmed at 0.6 ml @0.5 ml/min (certain experiments involved 4separate washes, each with 0.5 ml PBS), or 1 wash with 1 ml PBS, volumeprogrammed at 1.0 ml @0.5 ml/min followed by final wash with 0.5 ml H₂O.

The elution cycle involved 4 in/out cycles, volume programmed at0.1-0.15 ml @1 ml/min (15 μl elution buffer, 111 mM NaH₂PO₄ in 14.8 mMH₃PO₄, pH 3.0).

To quantitate the IgG recovered in the procedure and to analyze itspurity, 15 μl elution volume was divided into two parts: 13 μl wasreacted with freshly prepared 13 μl of 10 mg/ml TCEP (final volume=26 μland [TCEP]=17.5 mM) at room temperature for ˜16 hours. 20 μl out ofabove 26 μl reduced IgG_(2a) was injected into a non-porous polystyrenedivinylbenzene reverse phase (C-18) column using an HP 1050 HPLC system.A gradient of 25% to 75% between solvent A which is 0.1% TFA in waterand solvent B which is 0.1% TFA in ACN was used for 5 minutes.Detection: UV at 214 and 280 nm. There are two major IgG_(2a) peakshaving similar intensities as shown in the data below, which elutedaround 3.17 and 3.3 min. Area under these two peaks was integrated from(3.13-3.5) min in each case and corresponding mAU was recorded at 214nm. Only first elution (15 μl) percent recovery was calculated.TCEP-treated IgG_(2a) a standards (injected amount 1.08, 2.16, 4.32,6.48 and 8.64 μg of FITC-MAb, obtained from Fitzgerald, Inc) underidentical reaction condition was loaded into the column and used as astandard curve for recovery calculation.

Summary data shown below from these experiments indicate that IgGpurification using the Protein A extraction columns was highlyselective. A 333-fold excess of BSA can quantitatively be removed in avery fast process.

Recoveries from Selectivity Assay (Determined by HPLC Method)

Amersham Repligen Recovery Experimental Procedure Recovery 49% 15 μgIgG_(2a)/0.5 ml PBS (2 cycles loading) 43% 64% 15 μg IgG_(2a)/0.5 mlPBS + 5 mg BSA (2 cycles 56% loading) 66% 15 μg IgG_(2a)/0.5 ml PBS + 5mg BSA (5 cycles 62% loading)

2 ul of the reduced IgG from each experiment was analyzed by SDS-PAGE,using a Nu-PAGE 4-12% Bis-Tris gel with MES running buffer (FIG. 14).Lane 1: marker; Lane 2: 2 μg BSA; Lane 3: 2 μg IgG_(2a); Lanes 4 and 5:RepliGen and Amersham Protein A resin only, respectively; Lanes 6, 7 and8: 2 μl each of RepliGen Protein A purified IgG_(2a) from PBS, PBScontaining 5 mg BSA (2 and 5 cycles loading), respectively; Lanes 9, 10and 11: 2 μl each of Amersham Protein A purified IgG_(2a) from PBS, PBScontaining 5 mg BSA (2 and 5 cycles loading), respectively.

Example 12 Comparison of Frit Backpressures

The backpressure was determined for a number of screen frits and porouspolymer frits using the following method. Referring to FIG. 19, a tipcolumn 308 comprising membrane frits 311 and 313 and a packed bed ofresin 312 was attached to the output tubing 314 of the system describedin the above example.

Initially, deionized water is pumped through the bed of extraction media312 at a constant flow rate as described in the previous example, andthe baseline backpressure is read off the pressure gauge once the flowand pressure have stabilized, i.e., reached equilibrium. The tip column308 functions to produce a baseline backpressure when deionized water ispumped through the system. To measure the back pressure of a particularmembrane frit, a membrane frit 320 is welded to the narrow end 322 of apipette tip 324, and the narrow end of the tip 322 is fitted into thewide open end 326 of tip column 308 to form a friction seal (See FIG.20). The flow and pressure are allowed to stabilize, and the increase inbackpressure relative to the baseline backpressure resulting fromaddition of the membrane is read off the pressure gauge.

In some experiments, the backpressure was determined for two or moremembrane screens attached in series. This was accomplished by frictionfitting two or more membrane-tipped pipette tips in series (324, 326 and328) and attaching to the tip column 308 (see FIG. 21). The increase inbackpressure resulting from the plurality of membranes is then read offthe gauge once equilibrium has been reached.

In a control experiment, it was determined that attachment of a pipettetip lacking a membrane frit (or several such pipette tips in series) inplace of pipette tip 324 did not result in any detectable increase inbackpressure. Hence any backpressure detected in the experiments is duesolely to the frit or frits.

In one set of experiments, the backpressure for a 1.5 mm diameter 37micron pore size polyester membrane frit (Spectrum Lab, Cat. No. 146529)was determined at a flow rate of 4 mL/min. The backpressures weredetermined for different single screens, and it was found that theaddition of these membranes resulted in an increase in backpressure of0.25, 0.3 and 0.3 kPa (1 psi=6.8948 kPa). Two screens were attached inseries, and found to result in total increase in an increase inbackpressure of 0.4 kPa. Three screens were attached in series, andfound to result in an increase in backpressure of 1.1 kPa. Thus, it wasconcluded that at a flow rate of 4 mL/min, the backpressure of one ofthese membranes frits is about 0.3 kPa.

In a separate experiment, it was shown that the relationship betweenbackpressure and flow rate is approximately linear. Hence, it can beextrapolated that at a flow rate of 1 mL/min (a typical flow rate whenthe frits are used in the context of a pipette tip extraction column)the backpressure of these membrane frits is about 0.3/4, or 0.075 kPa.

In another set of experiments, the relation between screen pore size,screen diameter and backpressure was assessed. Polyester membrane fritshaving pore sizes of 15 micron (Spectrum Lab, Cat. No. 145832), 21micron (Spectrum Lab, Cat. No. 145833) and 37 micron (Spectrum Lab, Cat.No. 146529) were tested. Two different diameter screens were prepared.The small screen diameter was approximately 0.85 mm and the large screendiameter was 1.4 mm. Because the screens were welded to the tip, theeffective diameter varied depending on how much the hot polypropyleneflowed from the edge into the screen. This affected the backpressure onthe smaller screen diameter much more than the large screen diameter.Three tips each were prepared for each pore size and for each diameter.The results were as follow:

-   1. Small screen, 15 μm, 1 mL/min-   Backpressure: 3.3, 2.7, 1.5 kPa-   2. Small screen, 21 μm, 4 mL/min-   Backpressure: 2.5, 6.3, 3.6 kpa (Therefore effective backpressure at    1 mL/min is extrapolated to be 0.63, 1.6, 0.90 kpascals)-   3. Small screen, 37 μm, 4 mL/min, stack of 3 in series-   Backpressure: 2.2 kPa (Therefore effective backpressure of one frit    at 1 mL/min is extrapolated to be 0.18 kpacals)-   4. Large screen, 15 μm, 1 mL/min, stack of 3-   Backpressure: 6.5 kPa (Therefore effective backpressure at 1 mL/min    is extrapolated to be 2.2 kpascals)-   5. Large screen, 21 μm, 4 mL/min, stack of 3 in series-   Backpressure: appr. 0.1 kPa (Therefore effective backpressure at 1    mL/min is extrapolated to be 0.0083 kpascals)-   6. Large screen 37 μm, 4 mL/min, stack of 3 in series-   Backpressure: appr. 0.05 kP (Therefore effective backpressure at    mL/min 0.0042 is extrapolated to be kpascals)

The back pressure was also determined for frits made from porous polymermaterial, similar to the types of frits used in more columnchromatography. The porous polymer frit were friction fit into pipettetips as shown in FIG. 22 (330 is the pipette tip and 332 is the frit),and the backpressure was determined using the same device andmethodology as described above for use with membrane frits. (Note thediameters of the frits reported are cut size. When the frit is pushedinto the tip body, the diameter will decrease. Larger starting diameterof frits had to be pushed more firmly into the pipette body to preventit from dislodging.)

All porous polymer frits tested were 1/16 inch thick, and varied indiameter and pore size. The materials tested were a 35 micron porehydrophilic polymer (3.4 and 4.4 mm diameter) obtained from ScientificCommodities (Lake Havasu City, Ariz., Cat No. BB2062-35L); a 15-45micron pore, UHMW Polypropylene polymer obtained from Porex (Cat. No.X-4900) and a 20-25 micron polypropylene polymer obtained from GenPore(Reading, Pa.). The measured backpressures are presented in thefollowing table. The backpressures are substantially higher than thoseseen with the membrane frits.

Pore size Frit diameter Flow rate Backpressure (micron) (mm) (mL/min)(kPa) 35 3.4 4 8.5 35 3.4 3 6.0 35 3.4 2 3.6 35 3.4 1 1.8 35 4.4 4 4.635 4.4 3 3.5 35 4.4 2 1.5 35 4.4 1 low 15-45 3.4 4 11.0 15-45 3.4 3 7.715-45 3.4 2 4.8 15-45 3.4 1 2.0 15-45 4.4 4 9.5 15-45 4.4 3 6.5 15-454.4 2 4.0 15-45 4.4 1 1.8 20-25 1.4 4 high 20-25 1.4 3 9.0 20-25 1.4 26.0 20-25 1.4 1 2.5

Example 13 Comparison of Column Backpressures

Column backpressure was determined for a number of pipette tip-basedcolumns using the following method. Referring to FIG. 19, an HP1050 pump302 (Hewlett-Packard) was configured such that the input tubing 304 issubmerged in deionized water 306. To measure the back pressure of aparticular tip column 308, the narrow end 310 of the tip column(containing packed bed 312 between membrane frits 311 and 313) is fittedinto the open end of the output tubing 314 to form a friction seal. Theoutput tubing includes a t-fitting 316 attached to a Marshall Townpressure gauge 318 with a range of 0-5 psi (0-34 kPa). The deionizedwater is then pumped through the packed bed 312 at a constant flow rate,and the back pressure is read off the pressure gauge once the flow andpressure have stabilized, i.e., reached equilibrium.

When the pump is first turned on, depending upon the backpressure of thecolumn, it can take a while for enough pressure to build up before waterstarts flowing through the column at a constant flow rate. Typically, inorder to reach equilibrium more quickly, the pump was initially run at afaster flow rate (e.g., 2 mL/min) and then backed off to the desiredrate (e.g., 1 mL/min) once the flow through the column had reached arate around the desired rate.

For some columns, the backpressure was determined at only 1 mL/min. Forother columns, backpressure was determined for a series of ascendingflow rates (e.g., 1, 2, 3 and 4 mL/min). For these experiments therelationship between flow rate and back pressure was found to beapproximately linear. For some of the smaller columns, the backpressureat 1 mL/min was so low that it could not be accurately measured with thepressure gauge used. In those cases, the back pressure was determined ata flow rate of 5 mL/min, and the backpressure at 1 mL/min calculatedbased on an assumed linear relationship between flow rate andbackpressure (as demonstrated for other columns). The backpressures arepresented in the following table. The C18 Zip Tip was obtained fromMillipore (Billerica, Mass.). The other tips are packed resin bedpipette tip columns manufactured as described herein. Column bodies weremade by modifying pipette tips obtained from several different vendors,including 200+ tips supplied by Packard/Perkin-Elmer (200+ PE), 200+tips provided by Rainin (200+ R), and 200+ tips designed to be used witha Zymark instrument (200+ Z). Each of the resin columns used 37 micronpolyester membrane from Spectrum Labs for the frit material, which waswelded onto the tip body. Ni-NTA agarose resin (Ni-NTA) was obtainedfrom Qiagen (Germany). Protein A Sepharose resin was (ProA) was obtainedfrom Repligen. Protein G agarose resin (ProG) was obtained from Exalpha.Glutathione Sepharose resin (Glu) was obtained from Amersham. Most ofthe tip columns had bed volumes of about 5 uL, except for three 200+Z-ProA tips that were prepared with bed volumes of about 1.25 uL, 0.62uL and 0.25 uL. Specific bed dimensions for the beds in each type ofcolumn are as follows: 200+ PE, bed length 2.4 mm, bed diameter 1.6-1.82mm, calculated bed volume of 5.5 uL; 200+ R bed length 2.3 mm, beddiameter 1.5-1.82 mm, calculated bed volume of 5.0 uL; 200+ Z bed length2.5 mm,, bed diameter 1.43-1.82 mm, calculated bed volume of 5.2 uL. Thesmaller bed volume tips had bed diameters of 1.75-1.82 mm, bed volumesof about 1.25 uL, 0.62 uL and 0.25 uL, corresponding to bed heights ofabout 0.5 mm, 0.4 mm and 0.3 mm, respectively.

Note that the Zip Tip columns have substantially higher backpressuresthan the tip columns comprising a packed bed of resin and membranefrits.

The effect of varying the tightness of bed pack was assessed bycomparing the backpressure of 200+ Z-ProA, 5.2 μL bed tips that werepacked tighter than the other beds. Note that tighter packing of the bedleads to substantially higher backpressures.

C18 Zip Tip mL/min 1.0 kpascals 28.0 200 + PE-Ni- NTA, 5.5 μL bed mL/min1.0 2.0 3.0 4.0 kpascals 2.4 4.9 8.0 11.3 200 + R-ProA, 5.0 μL bedmL/min 1.0 kpascals 2.5 200 + R-Ni- NTA, 5.0 μL bed mL/min 1.0 kpascals2.5 200 + PE-ProA, 5.5 μL bed mL/min 1.0 kpascals 1.7 200 + PE-ProG, 5.5μL bed mL/min 1.0 kpascals 1.8 200 + R-Glu, 5.0 μL bed mL/min 1.0kpascals 3.2 200 + R-ProG, 5.0 μL bed mL/min 1.0 2.0 3.0 4.0 kpascals2.5 3.6 5.8 8.2 200 + Z-ProA, A, tighter bed B, tighter bed 5.2 μL bedmL/min 1.0 1.0 kpascals 18.5 50 200 + Z-ProA, 1.25 μL bed mL/min 1.0 2.03.0 4.0 kpascals 1.1 2.3 3.5 4.6 200 + Z-ProA, 0.62 μL bed mL/min 5.01.0 kpascals 2.0 0.4* 200 + Z-ProA, 0.25 μL bed mL/min 5.0 1.0 kpascals0.4 0.08* *Values extrapolated from 5.0 mL/min pressure.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications and this application is intended to cover and variations,uses, or adaptations of the invention that follow, in general, theprinciples of the invention, including such departures from the presentdisclosure as come within known or customary practice within the art towhich the invention pertains and as may be applied to the essentialfeatures hereinbefore set forth. Moreover, the fact that certain aspectsof the invention are pointed out as preferred embodiments is notintended to in any way limit the invention to such preferredembodiments.

1. A method of extracting an analyte from a solution comprising thesteps of: a. passing a solution containing an analyte back and forththrough a pipette tip column, wherein the pipette tip column iscomprised of: i. a column body having an open upper end, an open lowerend, and an open channel between the upper and lower ends of the columnbody, ii. a bottom frit bonded to and extending across the open channel,iii. a top frit bonded to and extending across the open channel betweenthe bottom frit and the open upper end of the column body, wherein thetop frit, bottom frit, and column body define the extraction mediachamber, wherein the top frit and the bottom frit are less than 350microns thick, wherein the bottom frit is a membrane screen and the topfrit is optionally a membrane screen, and wherein the membrane screen isselected from a group of materials consisting of nylon, polyester,polyamide, polycarbonate, cellulose, polyethylene, nitrocellulose,cellulose acetate, polypropylene, polysulfone, and glass, and iv. a bedof extraction media having a bed volume, whereby analyte adsorbs to saidextraction media; and b. eluting the analyte by aspirating anddischarging a desorption solvent through the pipette tip column, andwherein said analyte is an active protein.
 2. The method of claim 1,wherein the volume of desorption solvent is in the range of about 10% toabout 300% of the bed volume.
 3. The method of claim 1, wherein step (a)is performed more than one time.
 4. The method of claim 1, wherein thebed volume is in the range of between 0.1 and 100 uL.
 5. The method ofclaim 1, wherein between step (a) and step (b), a quantity of washsolution is aspirated and discharged through the extraction media. 6.The method of claim 1, wherein step (b) is performed more than one time.7. The method of claim 1, wherein the extraction media comprises anaffinity binding agent.
 8. The method of claim 1, wherein the bed ofextraction media comprises a packed bed of gel resin beads.
 9. themethod of claim 8, wherein the gel resin beads are agarose beads orsepharose beads.
 10. The method of claim 1, wherein the bottom frit hasa pore volume of 1 microliter or less.
 11. The method of claim 1,wherein the bottom frit is less than 200 microns thick.
 12. The methodof claim 1, wherein the upper end of the column body is attached to apump for aspirating fluid through the lower end of the column body. 13.The method of claim 12, wherein the pump is a pipettor, a syringe, or aperistaltic pump.